A 68-year-old fair-skinned male farmer presents with a 2.5 cm indurated, hyperkeratotic nodule on the dorsal surface of his left hand with a 4-month history of growth and occasional bleeding. Biopsy confirms invasive squamous cell carcinoma with perineural invasion. The lesion marked **A** in the diagram represents this cutaneous squamous cell carcinoma. Which of the following best describes the pathogenesis and metastatic risk profile of the lesion marked **A**?

Question

Accepted Answer

B. Arises from cumulative UVB-induced TP53 mutations in keratinocytes with 2–5% overall metastatic potential, rising to >25% in high-risk subgroups such as those with perineural invasion. ## Why Option 1 is correct

The structure marked **A** (cutaneous squamous cell carcinoma) pathogenesis is fundamentally rooted in cumulative UVB radiation, which causes characteristic thymine dimer formation and TP53 mutations in epidermal keratinocytes. The clinical anchor specifies that cSCC has a baseline metastatic potential of 2–5% overall, but this rises dramatically to >25% in high-risk subgroups—including tumors with perineural invasion (as present in this patient), large size (≥2 cm), location on lip/ear, poor differentiation, and immunosuppression. The presence of perineural invasion in this case places the lesion in the high-risk category. This is the defining pathobiologic and clinical risk profile of cSCC per Bolognia Dermatology 5e Ch 108 and NCCN guidelines.

## Why each distractor is wrong

- **Option 2**: While HPV-16 is indeed a risk factor for periungual and anogenital SCC, it is NOT the primary driver of cutaneous SCC on sun-exposed skin (hand in this case). Moreover, HPV-associated cSCC does not have <1% metastatic potential—high-risk features still apply. This conflates anogenital SCC biology with cutaneous SCC.
- **Option 3**: Although arsenic exposure is a recognized risk factor for cSCC, it is not the primary pathogenic mechanism in a sun-exposed occupational exposure case (farmer with dorsal hand lesion). Arsenic-induced cSCC does not have a lower metastatic risk than UV-induced disease, and perineural invasion is still a major risk escalator regardless of etiology.
- **Option 4**: cSCC does not arise from "spontaneous dedifferentiation" but from stepwise progression through actinic keratosis and carcinoma in situ driven by cumulative UV damage. A 30–40% metastatic rate is far too high and not supported by literature. Risk is NOT uniform across all sites—lip and ear cSCC carry substantially higher metastatic risk.

**High-Yield:** cSCC = UV-driven TP53 mutations → 2–5% baseline metastasis, but >25% in high-risk (perineural invasion, lip/ear, large, immunosuppressed).

[cite: Bolognia Dermatology 5e Ch 108; NCCN Squamous Cell Skin Cancer 2024]

Answer

A. Arises from spontaneous keratinocyte dedifferentiation with 30–40% metastatic potential and uniform risk across all anatomic sites

Answer

C. Arises from chronic arsenic exposure causing RAS activation with 10–15% metastatic potential and no increased risk with perineural invasion

Answer

D. Arises from HPV-16 integration causing CDKN2A loss with <1% metastatic potential and excellent prognosis regardless of size or location

Explanation

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