Non-melanoma skin cancers

Basal Cell Carcinoma - The Pearly Peril

• Most common skin cancer. Locally invasive, very low metastatic potential.
• Risk Factors: Chronic sun exposure (UVB), fair skin, immunosuppression, xeroderma pigmentosum.
• Subtypes:
  • Nodular: Most common. Pearly papule with telangiectasias.
  • Superficial: Pink/red patch with fine scale.
  • Morpheaform: Scar-like, indistinct borders, aggressive.
• Histology: Nests of basaloid cells in the dermis with peripheral palisading nuclei and stromal retraction.

⭐ Classic "rodent ulcer" describes central ulceration within a pearly, rolled border.

• Treatment: Mohs surgery for high-risk/facial lesions. Standard excision, curettage, or topical therapies for others.

Squamous Cell Carcinoma - Keratin's Rebellion

• Pathogenesis: Malignant proliferation of epidermal keratinocytes, invading the dermis. Often arises from a precursor lesion, actinic keratosis.
• Risk Factors: Chronic UVB exposure, immunosuppression (e.g., transplant recipients), chronic inflammation (e.g., burn scars, Marjolin's ulcer), arsenic, HPV.
• Clinical: Firm, scaling, erythematous papule or plaque; may ulcerate or bleed. Typically on sun-exposed areas like the face, lower lip, ears, and hands.
• Histology: Invasive cords/nests of atypical squamous cells with eosinophilic cytoplasm, large pleomorphic nuclei, and characteristic keratin pearls.
  • Bowen's Disease: SCC in situ (full-thickness epidermal atypia).

⭐ SCC arising in non-sun-exposed sites, such as chronic wounds or burn scars (Marjolin's ulcer), has a higher metastatic potential.

Precursors & Mimics - The Warning Signs

• Actinic Keratosis (AK)

  • Premalignant lesion for SCC; rough, "sandpaper" feel.
  • Found on sun-exposed skin (face, scalp, arms).
  • Progression risk to SCC is low per lesion (<1%/year) but high per patient.

• Bowen's Disease (SCC in situ)

  • Full-thickness epidermal atypia without dermal invasion.
  • Well-demarcated, scaly, erythematous patch or plaque.

• Keratoacanthoma (KA)

  • Rapidly growing "volcano-like" nodule with a central keratin plug.
  • Often spontaneously involutes; treated as well-differentiated SCC.

⭐ Leser-Trélat Sign: Sudden eruption of multiple seborrheic keratoses can be a sign of underlying internal malignancy, most commonly gastric adenocarcinoma.

Rarer Tumors - The Odd Ones Out

• Merkel Cell Carcinoma: Aggressive neuroendocrine tumor, often on sun-exposed skin. Associated with Merkel cell polyomavirus. Histology shows small blue cells; stains for synaptophysin & CK-20.
• Dermatofibrosarcoma Protuberans (DFSP): Locally aggressive, slow-growing spindle cell tumor. Histology: storiform (pinwheel) pattern, CD34 positive.
• Sebaceous Carcinoma: Arises from sebaceous glands, typically on the eyelid. Associated with Muir-Torre syndrome (Lynch syndrome variant).

⭐ Merkel cell carcinoma presents as a rapidly growing, painless, red-to-violaceous nodule (AEIOU mnemonic: Asymptomatic, Expanding rapidly, Immunosuppression, Older age, UV-exposed site).

High‑Yield Points - ⚡ Biggest Takeaways

• Basal Cell Carcinoma (BCC) is the most common skin cancer, presenting as a pearly papule with telangiectasias and showing peripheral palisading on histology.
• Squamous Cell Carcinoma (SCC) is linked to UV exposure and immunosuppression; histology reveals characteristic keratin pearls.
• Actinic keratosis is the most common premalignant lesion for SCC.
• Keratoacanthoma is a rapidly growing, volcano-like SCC variant that can spontaneously regress.
• Marjolin's ulcer is an aggressive SCC arising in chronic wounds or burn scars.