Dermatologic Oncology
Scope
Expect questions on keratinocyte carcinomas, melanoma, Merkel cell carcinoma, dermatofibrosarcoma protuberans, sebaceous carcinoma, and Kaposi sarcoma, with emphasis on risk factors, histologic diagnosis, margins, and systemic therapy.
Core rules
- Basal cell carcinoma: PTCH1 pathway activation; nodular, superficial, morpheaform subtypes; morpheaform behaves aggressively; Hedgehog inhibitors for advanced disease.
- Squamous cell carcinoma: ultraviolet exposure, actinic keratosis, Bowen disease, chronic wounds; high-risk features include depth, perineural invasion, immunosuppression.
- Melanoma: Breslow thickness and ulceration are the strongest prognostic factors; sentinel node biopsy for appropriate thickness; BRAF testing for advanced disease.
- Merkel cell carcinoma: CK20 dot-like positivity; associated with Merkel cell polyomavirus; PD-1 blockade is effective.
- Dermatofibrosarcoma protuberans: COL1A1-PDGFB fusion; CD34 positive; imatinib for unresectable disease.
- Mohs surgery for high-risk, recurrent, or cosmetically sensitive tumors.
Worked example
A 70-year-old has a pearly papule with rolled border and telangiectasia on the nose. Reasoning: morphology favors nodular BCC. Biopsy confirms. Because the nose is high-risk and tissue-sparing is important, Mohs micrographic surgery is preferred over routine excision.
Traps
Use Breslow thickness, not Clark level, for melanoma staging. Sebaceous carcinoma requires evaluation for Muir-Torre syndrome. A non-healing ulcer in an old scar may be SCC, not infection.