Skin Cancer - Board Review Summary

PART I - KERATINOCYTE CARCINOMA: EARLY BCC AND cSCC

Management Paradigm + Dose Anchors

Clinical lane	Board approach	RT / dose anchor
Low-risk BCC or cSCC	Surgery or Mohs is usually preferred when morbidity is low. Definitive RT is excellent for nonsurgical candidates, cosmetically sensitive sites, or patients prioritizing function and cosmesis.	Small/superficial lesions often 35 Gy / 5, 40-45 Gy / 10, or 45-50 Gy / 15. Larger lesions usually need more fractionation: 50-55 Gy / 20 or 60-66 Gy / 30-33.
Cosmetically sensitive anatomy	Nose, lip, eyelid, external ear, and selected facial lesions may be strong RT candidates if surgery would be deforming or functionally costly. Mohs remains a major comparator.	Use fractionation that protects cosmesis, cartilage, and late fibrosis. Avoid very large fraction size near cartilage, eyelid, nasal ala, or lip unless the patient is frail and the goal is convenience.
Target design	Confirm the biopsy site. Use clinical exam, photos, dermoscopy when available, scar map, and imaging if depth or named-nerve spread is uncertain.	Typical CTV is 5-15 mm. Choose larger margins for cSCC, tumors >2 cm, recurrent disease, infiltrative/desmoplastic histology, high-risk subtype, or poorly defined borders.
Technique choice	Electrons, superficial/orthovoltage, photons, and brachytherapy can all work when depth, surface dose, setup reproducibility, shielding, and cosmesis are respected.	Bolus or surface-prescription strategy must match the modality. Do not underdose deep cartilage, bone, orbital, or perineural extension with a superficial setup.
Local recurrence after prior therapy	Re-biopsy and restage. Mohs or re-excision if feasible; RT if not previously irradiated; re-irradiation only after careful anatomy, prior dose, and expected benefit review.	Curative re-RT is individualized. Palliation commonly uses 8 Gy x 1, 20 Gy / 5, or 30 Gy / 10.

BCC vs cSCC: The High-Yield Contrast

Feature	BCC	cSCC
Frequency	More common; most keratinocyte carcinomas	Less common, but more dangerous biologically
Clinical tempo	Typically months to years	Often weeks to months
Metastatic risk	<<<1%	About 4% overall, but much higher in very high-risk groups
Relative radiosensitivity	More radiosensitive	Less radiosensitive than BCC, but still often well controlled with appropriate RT
Systemic backbone for advanced disease	Hedgehog pathway inhibitors such as vismodegib or sonidegib; cemiplimab after HHI progression/intolerance or when HHI is inappropriate	PD-1/PD-L1 pathway therapy: cemiplimab, pembrolizumab, and cosibelimab in appropriate advanced settings
Board trap	Do not ignore neglected BCC: bone, orbit, skull base, and deep soft-tissue invasion can still be devastating.	Do not treat cSCC like low-grade skin-only disease when it has depth, PNI, immunosuppression, poor differentiation, or nodal risk.

Subtype Matters

Histology	Lower-risk subtypes	Higher-risk subtypes
BCC	Nodular, superficial, pigmented, fibroepithelial, infundibulocystic	Micronodular, infiltrating, sclerosing / morpheaform, basosquamous, sarcomatoid
cSCC	Keratoacanthoma, verrucous	Poorly differentiated, spindle cell, acantholytic, adenosquamous, clear cell, desmoplastic, metaplastic

Prevention, Workup, and Imaging

Risk factors: UV exposure, fair skin, older age, male sex, prior skin cancer, chronic wounds/burn scars, prior radiation, HPV-related lesions, genetic susceptibility syndromes, and immunosuppression.
Immunosuppression: transplant and hematologic malignancy patients have higher recurrence/metastasis risk. Checkpoint inhibitors may carry special risk in solid-organ transplant recipients, so local control strategy matters.
Workup: full skin and nodal exam, biopsy confirmation, careful review of prior procedures, and explicit neurologic symptom review for PNI.
Image when: lesion is fixed to fascia/muscle/bone, periorbital or skull-base extension is possible, named-nerve PNI symptoms are present, clinically suspicious nodes exist, or disease is locally advanced. MRI with contrast is favored for PNI and skull base; CT helps bone and nodal anatomy; PET/CT is reasonable for N+ or very high-risk advanced disease.

Early RT Randomized Experience

Study	Disease	Dose / technique	Outcome
Hall 1986	BCC	35 Gy / 5, 41.5 Gy / 7, or 37.5 Gy / 10; 130 kV	About 4% recurrence at 2 years
Landthaler 1989	BCC	60 Gy / 20 or 48 Gy / 12; 50 kV	About 10% and 8% recurrence at 3+ years
Landthaler 1989	cSCC	60 Gy / 20 or 48 Gy / 12; 50 kV	About 4% and 15% recurrence at 3+ years
Avril 1997	BCC	Ir-192 brachy 65-75 Gy / 5-7 d; 50 kV 36-40 Gy / 2; 85-250 kV 60-65 Gy / 15-35	4-year recurrence about 9%, 7%, and 5%
Garcia-Martin 2011	Periocular BCC	40-70 Gy / 10-15; 50-100 kV	0% recurrence at 2 years in a small series

Practical modality point: external-beam teletherapy remains the most common RT approach for early keratinocyte carcinoma. Brachytherapy can be useful in selected anatomy, but the modality decision should be driven by depth, geometry, reproducibility, and normal-tissue risk rather than tumor size alone.

Target and Technique Pearls

Step	Board-review pearl
GTV	Define from visible/palpable disease, scar/biopsy map, clinical photographs, and dermatology input when borders are subtle. Include the whole abnormal surface and subcutaneous component.
CTV	Typical range 5-15 mm. Expand more for cSCC, recurrent disease, tumor >2 cm, high-risk histology, or indistinct borders. Constrain thoughtfully at natural barriers only when invasion is not suspected.
Electrons	Wire field edge and scar, use bolus intentionally, prescribe to an appropriate isodose line, and choose energy to cover the deepest disease plus margin. Remember surface dose and lateral penumbra; use skin collimation and eye shielding when needed.
Orthovoltage / superficial	Excellent for shallow lesions. Choose kV by treatment depth and shielding. Avoid this approach when tumor thickness, cartilage/bone invasion, or PNI requires deeper coverage.
Photons / IMRT / protons	Best when the target includes nodes, named nerves to skull base, orbit-adjacent deep extension, parotid, or complex postoperative anatomy. Use bolus for skin dose unless the beam arrangement or proton range already assures adequate surface coverage.
Oral cavity / eye protection	Use eye shields when appropriate, oral stents to displace tongue or shield mucosa, and dental evaluation when high-dose fields approach mandible/maxilla.

PART II - HIGH-RISK AND RESECTABLE cSCC

Management Paradigm + Dose Anchors

Clinical lane	Board approach	RT / dose anchor
High-risk primary, resectable	Mohs or wide excision with attention to depth, differentiation, LVI, PNI caliber, margin status, recurrence, and immune status. PORT is favored for very high-risk pathology, positive/close margins not correctable, desmoplasia, large-caliber or named-nerve PNI, recurrent disease, or deep invasion.	Postop primary bed often 50-60 Gy for microscopic risk; escalate toward 60-66 Gy for positive margin, gross residual concern, ENE, or very high-risk features.
Clinically node-positive / parotid-positive	Therapeutic dissection or parotidectomy plus adjuvant RT is the classic standard. Treat parotid and neck thoughtfully for lateral face, scalp, temple, forehead, ear, and preauricular primaries.	Elective nodal basin about 50-54 Gy; involved nodal bed 56-60 Gy; ENE or gross residual risk 60-66 Gy.
Very high-risk after surgery + RT	Adjuvant cemiplimab is now a postoperative option for adults at high risk of recurrence after surgery and radiation. This is systemic intensification after completion of local therapy, not a substitute for indicated RT.	C-POST-style schedule: cemiplimab 350 mg q3wk initially, then 700 mg q6wk, or 350 mg q3wk throughout, up to about 48 weeks.
Borderline resectable or high-morbidity surgery	Neoadjuvant PD-1 therapy can produce major pathologic responses. Outside a response-adapted protocol, surgery and final pathology still drive PORT decisions.	Response-adapted postop RT frameworks commonly use about 56.1-63 Gy / 30, with elective nodal irradiation often favored for lateralized high-risk tumors.

AJCC 8 vs BWH Staging for Head and Neck cSCC

System	How to remember it	Board trap
AJCC 8 T staging	T1 ≤2 cm; T2 >2 to <4 cm; T3 ≥4 cm or minor bone erosion, deep invasion beyond fat / >6 mm, or PNI of a nerve ≥0.1 mm; T4a gross cortical bone or marrow invasion; T4b skull base or skull-base foraminal involvement.	AJCC T3 captures size, depth, PNI caliber, and minor bone erosion. T4 is gross major structure involvement, not just "high risk."
BWH high-risk factors	Four factors: diameter ≥2 cm, poor differentiation, PNI ≥0.1 mm, and invasion beyond subcutaneous fat. T1 = 0, T2a = 1, T2b = 2-3, T3 = 4 factors or bone invasion.	BWH T2b/T3 is the practical "very high-risk" bucket for nodal risk, imaging consideration, and adjuvant therapy discussion.
Why both matter	AJCC is the formal staging language; BWH is often more discriminating for cSCC risk stratification.	They do not map perfectly. In oral boards, state both the formal stage and the high-risk features driving management.

Primary-Site Local Recurrence Risk After Margin-Negative Excision

Risk factor	Observed risk	High-yield interpretation
Deep invasion	About 12% if thickness >6 mm	Depth is a major local and regional risk driver.
Desmoplasia / PNI / LVI	About 24% if desmoplastic	Neurotropic and desmoplastic features are especially concerning.

Risk Factors for Regional Nodal Recurrence

Factor	Approximate regional recurrence risk	Board use
Thickness 2-6 mm	4%	Usually not enough alone to mandate elective nodal RT.
Thickness >6 mm	16%	Begins to enter a range where nodal imaging and elective management are reasonable to discuss.
Immunosuppression	16%	Raises the stakes for local/regional control.
Diameter ≤2 cm	2%	Low nodal risk if no other high-risk features.
Diameter 2-5 cm	8%	Intermediate risk; combine with other features.
Diameter >5 cm	20%	Very high-risk primary; nodal evaluation matters.
Ear primary	10%	Think parotid/preauricular drainage and named nerve routes.

Adjuvant RT After Excision of High-Risk Primary cSCC

In a high-risk primary cSCC surgery plus adjuvant RT series, local recurrence was uncommon overall. The failures clustered in margin-positive cases treated with postoperative doses below 60 Gy. Practical board point: for positive margins, gross residual concern, or multiple very high-risk features, do not undertreat with a low microscopic-risk dose.

Postoperative RT Indications to Memorize

Setting	RT indication logic
Primary bed	Positive margin not correctable, close margin with high-risk features, recurrent tumor, BWH T2b/T3, AJCC T3/T4, deep invasion >6 mm/beyond fat, cartilage/bone/muscle invasion, desmoplasia, LVI, large-caliber PNI, named-nerve PNI, or immunosuppression.
Parotid / neck	Clinically involved parotid or neck nodes, multiple nodes, node >3 cm, ENE, recurrent nodal disease, in-transit disease, or high-risk lateral face/scalp/ear primary with meaningful occult nodal risk.
When not to reflexively treat	Low-risk, margin-negative, small cSCC without depth, poor differentiation, PNI, recurrence, immunosuppression, or nodal concern usually does not need PORT.

Perineural Invasion: Small Nerve vs Named Nerve

Incidental microscopic PNI: risk depends on nerve caliber, depth, multifocality, symptoms, and other tumor factors. Tiny superficial nerve PNI alone is not the same as clinical PNI.
Clinical or radiographic PNI: pain, paresthesia, numbness, facial weakness, diplopia, formication, or MRI enhancement along a nerve should trigger named-nerve mapping.
Targeting principle: treat the involved nerve pathway proximally toward the skull base when named-nerve spread is present. V1 tracks to orbital apex/superior orbital fissure/cavernous sinus; V2 to foramen rotundum; V3 including auriculotemporal nerve to foramen ovale; VII through parotid/stylomastoid foramen/facial canal depending extent.
Auricular trap: ear, temple, preauricular, and lateral cheek tumors may involve parotid drainage and sensory nerve pathways; do not draw a simple skin circle if symptoms or imaging suggest deeper spread.

Concurrent Chemotherapy and Postoperative Systemic Therapy

Porceddu / TROG 05.01: weekly carboplatin added to postoperative RT for high-risk cSCC did not improve locoregional control, disease-free survival, or overall survival. This remains the classic "do not reflexively add chemotherapy" board point.

C-POST: adjuvant cemiplimab after surgery and radiation improved DFS in high-risk cSCC and became a postoperative systemic option for adults at high risk of recurrence after completion of local therapy. Median DFS was not reached with cemiplimab versus about 49 months with placebo, with HR about 0.32. It intensifies treatment after indicated RT; it does not replace surgery or RT.

Neoadjuvant Immunotherapy in Resectable cSCC

Neoadjuvant PD-1 therapy can produce major pathologic responses in resectable high-risk cSCC, especially when surgery would be morbid. The unsettled board question is how to adapt adjuvant RT after a major pathologic response. Until response-adapted strategies mature, final pathology, margin status, PNI, depth, nodal disease, and immune status still drive PORT decisions.

Risk Stratification Beyond Clinicopathologic Features

40-gene expression profiling can stratify metastasis risk retrospectively, with approximate classes around low, intermediate, and high metastatic risk. It is promising for discussion, but clinicopathologic features still anchor standard board decisions until prospective treatment-selection data are definitive.

PART III - LOCALLY ADVANCED OR UNRESECTABLE KERATINOCYTE CARCINOMA

Management Paradigm + Dose Anchors

Clinical lane	Board approach	RT / dose anchor
Unresectable / medically inoperable cSCC	Multidisciplinary decision among definitive RT, PD-1/PD-L1 therapy, or combined/sequenced therapy. RT remains important for bleeding, pain, cranial nerve symptoms, orbit/skull-base threat, fungating disease, or potentially curable local disease.	Curative-intent gross disease often 66-70 Gy conventionally fractionated. Prospective platinum CRT used 70 Gy / 35.
Advanced BCC	Hedgehog inhibitor first when appropriate; cemiplimab after HHI progression/intolerance or if HHI is inappropriate. RT can be definitive, consolidative, or palliative depending on anatomy and response.	Definitive RT commonly 60-70 Gy. Vismodegib plus RT has prospective phase II support in selected unresectable head and neck BCC.
Threatening local symptoms	Use RT promptly for bleeding, pain, wound burden, cranial neuropathy, impending ulceration, or structural threat even when systemic therapy is planned.	Durable palliation often 30 Gy / 10 or 20 Gy / 5; frail/rapid palliation 8 Gy x 1.
Clinical-trial frontier	RT plus immunotherapy or targeted therapy is the major modern question. Do not assume that partial-site SBRT to one lesion reliably improves systemic immunotherapy outcomes.	Trial schemas range from 50-70 Gy with PD-1/PD-L1, HHI, or chemoimmunotherapy combinations.

Systemic Therapy Anchors for Advanced Keratinocyte Carcinoma

Disease	Current systemic anchor	Board nuance
Locally advanced or metastatic cSCC not curable with surgery/RT	Cemiplimab and pembrolizumab are key PD-1 options; cosibelimab is a PD-L1 option for metastatic or locally advanced cSCC when curative surgery or curative RT is not feasible.	Systemic therapy is central for unresectable disease, but local RT is still important for symptoms, threatening anatomy, and selected durable-control goals.
Advanced BCC	Vismodegib or sonidegib; cemiplimab after hedgehog inhibitor failure/intolerance or when HHI is inappropriate.	BCC and cSCC are not interchangeable. BCC is more HHI-driven; cSCC is more checkpoint-driven.
Transplant recipients	Coordinate with transplant and medical oncology. Checkpoint blockade can risk allograft rejection; selected protocols use immunosuppression modification.	Boards like this nuance: the "right drug" in the average patient may be hazardous in a transplant recipient.

RT Alone or Chemoradiation for Unresectable cSCC

Evidence lane	Population / dose	High-yield result
Advanced primary RT series	T3/4 primaries, often 55-75 Gy	RT controls roughly half of very advanced primary cSCC overall; BCC tends to control better than cSCC.
Nottage prospective CRT	Unresectable cSCC, platinum with 70 Gy / 35 fx	Grade 3-4 adverse events about 47%; complete response in about 53% of assessable patients.

Prospective RT + Biologic Therapy Studies

Study	Approach	Board-style takeaway
UNSCARRed	63-66 Gy / 30 + avelumab, then avelumab	Formal evaluation of RT plus PD-L1 blockade for unresectable stage I-IVA cSCC.
RAMPART	Neoadjuvant cemiplimab, then response-adapted RT 50-70 Gy / 25-35 plus immunotherapy	Reflects response-adapted integration of RT and PD-1 blockade.
CRIO	Platinum CRT plus immunotherapy; RT 54-70 Gy / 35	Explores trimodality systemic intensification in unresectable disease.
Vismodegib + RT	Selected unresectable head and neck BCC treated with hedgehog inhibitor plus RT	Combined targeted therapy plus RT can produce durable control in carefully selected BCC.

Bottom line for unresectable keratinocyte carcinoma: RT remains a major local therapy, but modern decision-making is histology-specific. For cSCC, checkpoint therapy is central; for BCC, hedgehog inhibition is central. RT is most valuable when local symptoms, function, bleeding, cranial nerves, orbit, bone, skull base, or durable local control matter.

PART IV - MELANOMA

Management Paradigm + Dose Anchors

Clinical lane	Board approach	RT / dose anchor
Primary cutaneous melanoma	Surgery is primary. RT is selective: lentigo maligna when unresectable or surgery is poor, desmoplastic/neurotropic or narrow-margin head and neck cases, positive margin not re-resectable, recurrence, or palliation.	Lentigo maligna RT often around 50-57.5 Gy in about 20-25 fractions; neurotropic melanoma trial regimen 48 Gy / 20.
Clinically detectable resectable stage III	Modern strategy increasingly favors neoadjuvant immunotherapy first, then response-adapted surgery/adjuvant therapy. Pathologic response strongly informs recurrence risk.	RT is not routine after major pathologic response. Consider nodal-basin RT for pathologic non-response, ENE, bulky/matted nodes, multiple nodes, parotid/cervical basin risk, or when regional control is crucial.
After lymphadenectomy, high-risk nodal basin	Nodal-basin RT improves regional control but not OS. Weigh lymphedema, fibrosis, and systemic therapy era context.	Classic anchors 48 Gy / 20 (TROG 02.01), 50 Gy / 28 (Mayo), or 30 Gy / 5 in selected older hypofractionated experiences.
Oligometastatic / palliative melanoma	Comprehensive metastasis-directed therapy to all known disease is different from single-lesion immune-priming SBRT. Use ablative RT selectively for durable control or symptom prevention.	Common SBRT varies by site; immunomodulatory trial example 24 Gy / 3. Palliative anchors 8 Gy x 1, 20 Gy / 5, 30 Gy / 10.

Melanoma Workup and Surgery Anchors

Topic	High-yield point
Biopsy	Excisional biopsy with narrow margins is preferred when feasible. Full-thickness punch or incisional biopsy is acceptable for special sites; superficial shave can compromise depth assessment.
Wide excision margins	In situ: 0.5-1 cm; ≤1 mm: 1 cm; 1.01-2 mm: 1-2 cm; 2.01-4 mm: 2 cm; >4 mm: 2 cm.
SLNB	Generally for T1b or thicker disease: >0.8 mm or <0.8 mm with ulceration. Consider for thinner tumors with adverse features such as young age, head and neck site, LVI, or high mitotic rate.
Completion dissection	After positive SLNB, completion dissection improves nodal control but not melanoma-specific survival in modern randomized data; ultrasound surveillance is often appropriate.
Imaging	Cross-sectional/PET imaging and brain MRI are most relevant for clinically node-positive, stage IIIB-D, symptomatic, or metastatic disease.

Primary-Site RT Indications in Melanoma

Consider primary-site RT for desmoplastic or neurotropic melanoma, especially head and neck tumors, positive margin not re-resectable, pathologic narrow margin with neurotropism, locally recurrent disease, or when surgery is not feasible. For a routine widely excised primary melanoma with clear margins and no neurotropism, RT is not standard.

Lentigo Maligna

Treatment	Diagnosis	Reported local recurrence range
Surgery	Lentigo maligna	5.6-15.4%
Surgery	Lentigo maligna melanoma	0-15.5%
RT	Lentigo maligna	1.6-38%
RT	Lentigo maligna melanoma	7.4-15.6%

Hong 2025: randomized unresectable lentigo maligna to imiquimod versus RT. The RT arm used a median dose around 54 Gy in about 25 fractions, commonly with superficial RT or electrons. Practical takeaway: for unresectable lentigo maligna, imiquimod and RT are both reasonable nonsurgical options, with treatment choice driven by extent, cosmesis, adherence, and response monitoring.

Reflectance confocal microscopy can help define field extent and assess response in lentigo maligna. A representative RT approach is 57.5 Gy / 23 fx with superficial photons, but there is no single mandatory dose.

Neurotropic / Desmoplastic Melanoma

Rare: neurotropic melanoma is <5% of cutaneous melanomas.
Typical phenotype: older patient, head and neck primary, frequent desmoplasia.
Biology: melanoma cells track along or into neural structures; local recurrence risk is high.
Board management: consider adjuvant RT after narrow-margin excision, named-nerve involvement, or unresectable microscopic risk.

RTN2 / Pinkham 2024: randomized patients after narrow-margin excision of neurotropic melanoma to adjuvant RT versus observation but closed early. The result supports a cautious board answer: consider adjuvant primary-site RT when neurotropic melanoma is excised with a narrow pathologic margin.

Adjuvant Nodal Basin RT After Lymphadenectomy for Melanoma

Trial / experience	Dose	Main result	Key toxicity
Mayo Clinic	50 Gy / 28 fx	No OS signal; historical support for regional control in selected high-risk basins	Mild lymphedema about 22%, severe about 7%
TROG 02.01	48 Gy / 20 fx	Regional recurrence about 18% vs 33% at 5 years; no OS benefit	Meaningful late toxicity and lymphedema risk
Hypofractionated nodal RT experience	30 Gy / 5 fx	High regional control in selected older series	Use cautiously near brachial plexus, bowel, skin folds, or high-risk lymphedema anatomy

Board pearl: melanoma nodal basin RT is mainly a regional control strategy, not a survival strategy. It is most defensible for ENE, bulky nodes, multiple involved nodes, large nodes, parotid/cervical risk, recurrent nodal disease, inadequate dissection, or pathologic non-response after neoadjuvant therapy.

Neoadjuvant Immunotherapy Era in Regionally Advanced Melanoma

Study	Regimen	pCR / pathologic response signal	Grade 3+ toxicity signal
SWOG S1801	Perioperative pembrolizumab vs adjuvant pembrolizumab	Improved event-free survival with neoadjuvant-first sequencing	Single-agent PD-1 toxicity range
NADINA	Neoadjuvant nivolumab + ipilimumab vs adjuvant nivolumab	High major pathologic response; pathologic responders did very well	Higher immune toxicity than single-agent PD-1
OPACIN-neo / PRADO	Nivolumab + ipilimumab variants	Higher pathologic response rates with optimized combinations	Combination intensity and toxicity must be balanced
Single-agent PD-1 neoadjuvant studies	Pembrolizumab or nivolumab	Lower pCR than combination therapy	Generally less grade 3+ toxicity

High-yield synthesis: neoadjuvant immunotherapy is now central for clinically detectable resectable stage III melanoma. More intensive combinations often increase pathologic response and toxicity. RT after neoadjuvant therapy is mainly considered for pathologic non-response or persistently high-risk nodal disease, not for every pathologic responder.

Oligometastatic Melanoma

Strategy	Key lesson
Non-comprehensive SBRT to 1-3 lesions with immunotherapy	SBRT such as 24 Gy / 3 can control treated lesions, but has not reliably improved systemic outcomes when only a subset of disease is irradiated.
Comprehensive metastasis-directed therapy	Treating all known sites with surgery/SBRT/ablation is a different concept and can be reasonable for carefully selected oligometastatic patients with controlled systemic disease.
AXIOM-style question	Randomized testing of SBRT to all extracranial lesions plus ICI is the cleaner way to test metastasis-directed therapy than partial-site immune-priming RT.

PART V - MERKEL CELL CARCINOMA

Management Paradigm + Dose Anchors

Clinical lane	Board approach	RT / dose anchor
Localized primary, operable	Wide excision + SLNB when feasible. Adjuvant RT is commonly favored because MCC is radiosensitive and locally/regionally aggressive, especially for head and neck, larger tumors, immunosuppression, LVI, close margins, or uncertain nodal assessment.	Negative-margin primary bed 50-56 Gy; microscopic positive margin 56-60 Gy.
Low-risk stage I	Observation after complete excision can be considered for very small, widely excised, node-negative tumors with reliable SLNB, especially outside head and neck.	If treating the primary bed, 50-56 Gy is common.
Definitive RT / nonsurgical	Definitive RT can be highly effective when surgery is morbid, disfiguring, or medically unsafe. Treat clinically involved nodes when present.	Gross primary or nodal disease usually 60-66 Gy; elective nodal basin commonly 46-50 Gy to 50-56 Gy depending risk.
Node-positive after dissection	Adjuvant nodal RT is strongest for multiple nodes, ENE, inadequate dissection, head and neck basin, or high recurrence concern. Chemotherapy is not routine adjuvant standard.	Nodal basin 50-56 Gy; boost ENE/residual-risk areas 56-60 Gy or gross disease 60-66 Gy.
Unresectable / metastatic	PD-1/PD-L1 therapy is central: avelumab, pembrolizumab, and retifanlimab are key approved agents. RT is used for local control, palliation, oligoprogression, and selected comprehensive ablative approaches.	Partial-site SBRT example 24 Gy / 3; palliative 8 Gy x 1, 20 Gy / 5, or 30 Gy / 10.

MCC Workup, Pathology, and Staging Hooks

Topic	Board-review hook
Clinical presentation	Rapidly growing, painless, red/purple nodule in an older or immunosuppressed patient. Head and neck and sun-exposed sites are common.
Pathology	Small blue cell tumor. CK20 paranuclear dot-like positivity supports MCC; TTF-1 negativity helps distinguish from small cell lung cancer.
Workup	Full skin/nodal exam, biopsy, SLNB when clinically node-negative, PET/CT or CT for staging, and MRI brain only when symptoms or advanced disease make it clinically relevant.
AJCC T stage	T1 ≤2 cm; T2 >2 to 5 cm; T3 >5 cm; T4 invades fascia, muscle, cartilage, or bone.
N and M stage	Separate occult nodal disease from clinically detected nodal disease; in-transit disease matters. M1a distant skin/subcutaneous/distant LN, M1b lung, M1c other visceral.

Localized Primary MCC: Surgery vs Definitive RT

Approach	Evidence signal	Takeaway
Wide excision	Large modern surgical series show very low local recurrence after excision.	Excellent local therapy when surgery is safe and not deforming.
Definitive primary RT	Crude local recurrence rates in definitive RT series are also low.	Appropriate for poor surgical candidates or anatomy where surgery would be morbid.
Adjuvant primary RT	Commonly used because MCC is radiosensitive and local/regional recurrence can be morbid.	Particularly favored for head and neck, close/positive margins, LVI, larger tumors, immunosuppression, and uncertain SLNB reliability.

Board pearl: for the MCC primary site, surgery or RT monotherapy can both be effective. The harder question is not whether RT works; it is when the incremental benefit of adjuvant RT outweighs field size, wound healing, frailty, and nodal management issues.

MCC Field Design and Dose

Primary bed: include scar and at-risk in-transit skin/subcutaneous routes. Traditional margins can be wide, often several centimeters when feasible, but head and neck fields are anatomically individualized.
SLNB-negative basin: nodal RT can often be omitted if SLNB was reliable. For head and neck primaries, discuss the higher false-negative concern and whether elective nodal RT is warranted.
Microscopic nodal disease: observation after complete dissection may be reasonable for a single microscopic node without ENE in selected patients; otherwise nodal RT is commonly used.
Gross disease: use definitive doses, typically 60-66 Gy, unless palliation or systemic therapy response changes intent.

Systemic Therapy and Adjuvant Immunotherapy

Setting	Board-review point
Advanced / recurrent / metastatic MCC	Avelumab, pembrolizumab, and retifanlimab are key approved checkpoint options. Chemotherapy can respond quickly but is less durable and is no longer the preferred durable systemic backbone.
Neoadjuvant immunotherapy	Neoadjuvant PD-1 therapy can produce pathologic responses in resectable MCC; response may inform recurrence risk, but local therapy decisions still require multidisciplinary judgment.
Adjuvant immunotherapy	Evidence is evolving. Do not omit indicated surgery, SLNB, or RT simply because postoperative immunotherapy is being considered.

Metastatic / Unresectable MCC After Anti-PD1/L1 Progression

In a randomized study of ipilimumab/nivolumab with or without non-comprehensive SBRT, MCC patients received 24 Gy / 3 fx to at least one but not all metastases. Second-line ipilimumab/nivolumab had an objective response rate around 31% and was not improved by SBRT. Treated lesions were controlled, but limited-site SBRT did not act as a reliable systemic immune enhancer.

CARTA Phase II

Feature	CARTA
Population	Metastatic or unresectable MCC progressing after first-line anti-PD1/L1 therapy
Strategy	Comprehensive ablative RT plus avelumab
N	17
ORR	71% (95% CI 44-90)
Median follow-up	18 months
Median PFS	7 months
Median OS	Not reached
Grade 3-4 treatment-related AEs	12%

Why CARTA is interesting: the evidence pattern suggests that comprehensive ablative RT plus immunotherapy may be more promising in refractory MCC than partial, non-comprehensive "immune-priming" SBRT to a subset of lesions.

PART VI - STAGING, PNI, AND TECHNIQUE QUICK HITS

Compact Oral-Board Checklist

Topic	Board-review hook
NCCN-style cSCC risk	High/very high-risk features include size and location, poor borders, recurrence, immunosuppression, prior RT/chronic inflammation, rapid growth, neurologic symptoms, poor differentiation, high-risk histology, depth, PNI, and LVI.
High-risk BCC	High-risk features include head and neck or high-risk anatomic location, large size, recurrent disease, poorly defined borders, immunosuppression, prior RT, morpheaform/infiltrative/micronodular/basosquamous histology, and PNI.
BWH cSCC staging	Four high-risk factors: diameter ≥2 cm, poor differentiation, PNI ≥0.1 mm, and invasion beyond subcutaneous fat. T2b/T3 is the classic very high-risk bucket.
AJCC 8 cSCC staging	Head and neck cSCC T3 includes tumor ≥4 cm, minor bone erosion, deep invasion, or PNI; T4a/T4b reflect gross cortical/marrow/skull-base/foraminal involvement.
Named-nerve / clinical PNI	Numbness, pain, paresthesia, weakness, diplopia, facial palsy, or formication matters more than incidental tiny-nerve PNI. Track named nerves to skull base when clinically/radiographically involved.
Auricular / parotid pathway	Ear, temple, lateral cheek, forehead, and scalp cSCC often drain to parotid/preauricular nodes before upper neck. For auricular tumors, remember facial nerve/parotid, auriculotemporal nerve to V3/foramen ovale, and great auricular/lesser occipital sensory pathways.
Elective nodal RT	Not routine for low-risk BCC/cSCC. Consider for very high-risk cSCC when nodal risk is substantial, especially ear/lip, recurrent disease, immunosuppression, poor differentiation, deep invasion, large-caliber PNI, or parotid-region primaries.
Skin setup / bolus	Wire visible disease, scar, biopsy site, and intended margin. Use photos and reproducible immobilization. For electrons/photons, bolus decisions determine surface dose; for superficial/orthovoltage, confirm depth coverage and shielding.
Cartilage / bone / orbit	Do not let a superficial technique underdose deep extension. CT/MRI is useful when cartilage, bone, orbit, skull base, or named-nerve PNI is suspected.
Wounds and fungating tumors	RT can palliate bleeding, pain, odor, and mass effect. Coordinate dressings, infection control, anticoagulation, and expected timing of response.

CROSS-CUTTING HIGH-YIELD POINTS

BCC vs cSCC: BCC is more common, slower, rarely metastatic, and more radiosensitive; cSCC metastasizes more often and is more checkpoint-sensitive systemically.
Advanced BCC systemic sequence: hedgehog inhibitor first when appropriate; cemiplimab after HHI failure/intolerance or when HHI is inappropriate.
Advanced cSCC systemic update: cemiplimab and pembrolizumab remain key PD-1 agents; cosibelimab is a PD-L1 option for metastatic/locally advanced cSCC not curable with surgery or RT.
Early-stage skin RT works well, with randomized and prospective series recurrence rates often in the single digits.
CTV for early skin cancer is clinical: usually 5-15 mm, larger for cSCC, lesions >2 cm, recurrent disease, and high-risk subtypes.
Image when the exam suggests more than skin: MRI for PNI/skull base/orbit/soft-tissue extension; CT for bone and nodal anatomy; PET/CT for N+ or very high-risk advanced disease.
BWH staging: cSCC high-risk factors are diameter ≥2 cm, poor differentiation, PNI ≥0.1 mm, and invasion beyond fat; T2b/T3 identifies a very high-risk group.
High-risk local recurrence factors in cSCC: depth >6 mm, desmoplasia, PNI, LVI, recurrence, and immunosuppression.
High-risk regional recurrence factors in cSCC: thickness, immunosuppression, larger diameter, and ear primary.
Auricular/lateral face cSCC: think parotid/preauricular drainage and named-nerve pathways, especially auriculotemporal nerve toward V3/foramen ovale.
Resectable high-risk cSCC: surgery plus adjuvant RT is standard; weekly carboplatin did not improve outcomes.
C-POST: adjuvant cemiplimab after surgery plus RT improves DFS in high-risk cSCC and is a postoperative systemic option.
Neoadjuvant cSCC immunotherapy: promising pathologic responses, but final pathology still drives postoperative RT outside mature response-adapted protocols.
Unresectable cSCC: RT alone controls only about half of very advanced primaries; combined systemic strategies are the modern area of interest.
Nottage chemoRT: 70 Gy / 35 with platinum gave substantial toxicity and complete response in about half of assessable patients.
Unresectable BCC: vismodegib plus RT is a real combined-modality option in selected head and neck cases.
Lentigo maligna: RT is a reasonable nonsurgical option; randomized data support considering RT or imiquimod in unresectable cases.
Neurotropic melanoma: rare, locally aggressive, usually head and neck, often desmoplastic; consider adjuvant RT after narrow-margin excision.
Melanoma nodal basin RT: improves regional control, not OS; lymphedema cost is real.
Neoadjuvant melanoma IO: more intensive combinations generally mean higher pathologic response and higher toxicity.
SWOG S1801 and NADINA: major reasons neoadjuvant sequencing is central in regionally advanced melanoma.
Adjuvant RT after neoadjuvant melanoma IO: mainly consider for pathologic non-response or persistently high-risk nodal disease.
Oligometastatic melanoma: comprehensive treatment of all sites is conceptually different from single-site immune-priming SBRT; the latter remains investigational.
MCC primary site: surgery or RT monotherapy can both be highly effective; adjuvant RT is commonly favored because MCC is radiosensitive and locally aggressive.
MCC systemic therapy: avelumab, pembrolizumab, and retifanlimab are key checkpoint options for advanced/recurrent disease.
Refractory metastatic MCC: limited-site SBRT did not clearly enhance ipilimumab/nivolumab, whereas comprehensive ablative RT plus avelumab in CARTA showed a strong response signal.
Palliative skin/MCC RT anchors: 8 Gy x 1, 20 Gy / 5, or 30 Gy / 10; choose by durability need, wound burden, symptoms, and prior RT.

CONSOLIDATED DOSE TABLE

Clinical setting	Dose / regimen	Why it matters
Early BCC (Hall)	35 Gy / 5, 41.5 Gy / 7, 37.5 Gy / 10	Classic kV randomized experience
Early BCC / cSCC (Landthaler)	60 Gy / 20 or 48 Gy / 12	High-yield historical skin RT fractionation
Early BCC (Avril, brachy)	65-75 Gy / 5-7 d	Interstitial brachy comparator
Early BCC (Avril, superficial RT)	36-40 Gy / 2	Very hypofractionated orthovoltage option
Early BCC (Avril, external beam)	60-65 Gy / 15-35	External-beam teletherapy benchmark
Common definitive low-risk skin RT	40-45 Gy / 10 or 45-50 Gy / 15	Practical anchor for small-to-moderate lesions
Common definitive larger/high-risk skin RT	50-55 Gy / 20 or 60-66 Gy / 30-33	More fractionated when size, depth, cosmesis, or late toxicity matter
Small-volume frail-patient skin RT	30 Gy / 3 once weekly or 20-25 Gy x 1	Convenience-oriented; use cautiously for cosmesis and late effects
Postop cSCC primary bed	50-60 Gy	Microscopic-risk postoperative range
Postop cSCC positive margin / ENE / residual-risk region	60-66 Gy	High-risk boost range
cSCC elective nodal basin	50-54 Gy	When nodal risk justifies elective treatment
cSCC involved nodal bed	56-60 Gy	Postoperative involved nodal-risk range
cSCC gross nodal / unresected residual disease	66-70 Gy	Curative-intent gross-disease anchor
Response-adapted adjuvant cSCC RT	56.1-63 Gy / 30	Representative postoperative framework after neoadjuvant immunotherapy
Unresectable cSCC chemoRT (Nottage)	70 Gy / 35	Prospective platinum chemoRT regimen
UNSCARRed	63-66 Gy / 30	RT plus avelumab for unresectable cSCC
RAMPART	50-70 Gy / 25-35	Response-adapted cemiplimab plus RT strategy
CRIO	54-70 Gy / 35	ChemoRT plus immunotherapy intensification
Definitive advanced BCC	60-70 Gy	Curative local therapy when surgery is not feasible
Lentigo maligna	50-57.5 Gy / 20-25	Common nonsurgical range; tailor to extent and modality
Neurotropic melanoma	48 Gy / 20	Trial-style adjuvant primary-site regimen
Melanoma nodal basin RT (Mayo)	50 Gy / 28	Historical randomized nodal RT regimen
Melanoma nodal basin RT (TROG 02.01)	48 Gy / 20	High-yield melanoma nodal-basin trial dose
Melanoma hypofractionated nodal RT	30 Gy / 5	Older selected experience; consider normal tissue carefully
Melanoma immunotherapy-modulation SBRT	24 Gy / 3	Non-comprehensive SBRT remains investigational
MCC adjuvant primary bed, R0	50-56 Gy	Common postoperative range
MCC microscopic positive margin	56-60 Gy	Postoperative escalation range
MCC gross/definitive disease	60-66 Gy	Primary or nodal gross disease
MCC elective nodal basin	46-50 Gy to 50-56 Gy	Depends on nodal risk and SLNB/dissection reliability
MCC partial-site SBRT	24 Gy / 3	Locally effective, not clearly systemically synergistic
Skin / melanoma / MCC palliation	8 Gy x 1, 20 Gy / 5, 30 Gy / 10	Symptom-directed common regimens

KEY LANDMARK TRIALS (memorize)

Trial / study	Disease	One-line takeaway
Hall 1986	Early BCC	Historical randomized kV RT data showing strong local control
Landthaler 1989	Early BCC / cSCC	60/20 and 48/12 are classic skin RT fractionations
Avril 1997	Early BCC	Brachytherapy and teletherapy produced good control; modality choice depends on anatomy and technique
Garcia-Martin 2011	Early periocular BCC	Small modern orthovoltage series with excellent short-term control
Brantsch 2008	cSCC risk stratification	Depth, size, ear site, and immunosuppression drive recurrence risk
Yan / Kim / Ma / Barker	High-risk primary cSCC	Adjuvant RT produced low local recurrence; sub-60 Gy failures in margin-positive disease stand out
Ruiz / Harris	High-risk cSCC	Adjuvant RT can improve control in selected BWH T2b/T3, PNI, and regional disease groups
Porceddu / TROG 05.01	High-risk resected cSCC	Adding weekly carboplatin to postoperative RT did not help
Gross 2022 / 2023	Neoadjuvant cSCC immunotherapy	Major pathologic responses are achievable; adjuvant RT adaptation remains nuanced
C-POST	High-risk resected cSCC after surgery + RT	Adjuvant cemiplimab improved DFS and is a postoperative systemic option
Nottage 2017	Unresectable cSCC	70 Gy / 35 platinum chemoRT is feasible but toxic
Barker 2024	Unresectable BCC	Vismodegib plus RT produced high response and durable local control in selected head and neck BCC
Hong 2025	Lentigo maligna	Randomized data support RT as a valid nonsurgical option
RTN2 / Pinkham 2024	Neurotropic melanoma	Supports considering adjuvant RT after narrow-margin excision
TROG 02.01	Node-positive melanoma after dissection	Nodal basin RT improves regional control, not survival, and increases toxicity
SWOG S1801	Regionally advanced melanoma	Neoadjuvant pembrolizumab sequencing beat purely adjuvant sequencing
NADINA	Regionally advanced melanoma	Neoadjuvant nivolumab/ipilimumab improved event-free outcomes; major pathologic response predicts excellent prognosis
PRADO / OpACIN-neo	Melanoma response-adapted therapy	Adjuvant RT is mainly considered for pathologic non-response or persistently high-risk disease
Spaas 2023	Oligometastatic melanoma	Single-site immunomodulatory SBRT remains investigational
AXIOM	Extracranial oligometastatic melanoma	Ongoing randomized test of SBRT to all lesions plus ICI
Kavanagh 2025	Primary MCC	Wide excision gave very low local recurrence in a large modern series
Gunaratne 2017	Primary MCC definitive RT	Definitive RT alone can achieve strong primary-site control
TROG 96.07	High-risk MCC	Historic chemoradiation experience; chemotherapy is not routine modern adjuvant standard
ADMEC-O / CheckMate 358	MCC immunotherapy	Adjuvant and neoadjuvant immunotherapy are evolving, but local therapy remains central
Kim 2023	Metastatic MCC after ICI	Partial-site SBRT did not clearly enhance ipilimumab/nivolumab, although irradiated sites were controlled
CARTA	Refractory metastatic MCC	Comprehensive ablative RT plus avelumab showed a strong response signal with manageable toxicity