Differential Diagnosis: Cutaneous Squamous Cell Carcinoma is the Primary Concern
In a 68-year-old fisherman with a rapidly enlarging, ulcerated lesion on a sun-exposed forearm, cutaneous squamous cell carcinoma (cSCC) should be at the top of your differential diagnosis, followed by keratoacanthoma, with epidermal cyst and pyogenic granuloma being far less likely given the clinical presentation.
Primary Differential: Cutaneous Squamous Cell Carcinoma
The clinical scenario strongly suggests cSCC based on multiple high-risk factors 1:
- Age and cumulative sun exposure: This 68-year-old man with frequent outdoor fishing represents the classic demographic—lifetime risk for men is 9-14% 1
- Occupational hazard: Fishermen experience significant UV exposure, with UV-B being primarily responsible for skin cancers 2
- Anatomic location: Sun-exposed areas like the forearm are common sites for cSCC in fair-skinned individuals 1
- Rapid growth with ulceration: These features are characteristic of invasive cSCC
The AAD guidelines emphasize that cSCC commonly develops on sun-exposed areas including the backs of arms and hands, precisely matching this presentation 1. Fishermen specifically show high incidence of non-melanoma skin cancers on sun-exposed areas, with studies documenting 9% basal cell carcinoma and 6% squamous cell carcinoma rates 3.
Secondary Consideration: Keratoacanthoma
Keratoacanthoma remains in the differential because it:
- Also presents as a rapidly growing lesion
- Occurs on sun-exposed skin in older adults
- Can ulcerate centrally
- May be clinically indistinguishable from cSCC
Critical pitfall: Many dermatopathologists now consider keratoacanthoma a variant of well-differentiated cSCC rather than a distinct entity, so treatment approach should be similar.
Less Likely Diagnoses
Epidermal cyst is unlikely because:
- These typically grow slowly over months to years, not rapidly
- They present as smooth, dome-shaped nodules, not ulcerated lesions
- Sun exposure is not a risk factor
Pyogenic granuloma is improbable because:
- These are vascular proliferations that typically follow trauma
- They present as friable, bleeding nodules rather than ulcerated plaques
- Rapid growth occurs over weeks, but the patient's age and sun exposure history don't fit the typical pattern
Immediate Action Required
Perform a biopsy immediately—either punch, shave, or excisional depending on lesion size 1. The AAD guidelines stress that appropriate treatment depends on accurate histologic diagnosis. Given the high-risk features (sun-exposed site, elderly patient, ulceration, rapid growth), this lesion requires tissue diagnosis before any definitive treatment planning.
Do not delay biopsy to observe the lesion, as cSCC can metastasize in approximately 3-5% of cases, with disease-related deaths exceeding 3,000 annually in the United States 1.