DISCUSSION
The pathology report shows a low-grade, well-differentiated squamous cell carcinoma (SCC)—in this case, a keratoacanthoma (KA). This common form of SCC is usually found on the sun-exposed skin of older patients. The lesions can range in size from 3 mm to 3 cm or larger and are usually round to oval and dome-like, with symmetrical architecture and, often, a central keratotic core. The differential includes cysts, warts, and seborrheic keratosis.
Histologically, KAs are composed of uniformly staining (blue) cells of similar size and shape (connoting relative benignancy), to which we apply the term well-differentiated. Poorly-differentiated cellular composition manifests with cells of different sizes, shapes, and colors; these characteristics suggest more aggressive malignancy.
Even though KAs are skin cancers, they are quite low-grade, which means they rarely metastasize; if left alone, they can resolve completely over time. However, their odd appearance and rapid growth are usually concerning enough to prompt their removal.
When suspected KAs are removed, it’s essential that the entire lesion be submitted for pathologic examination. This allows for the architecture of the entire lesion—its cellular composition and margins—to be evaluated. When only part of the lesion is removed for biopsy, the diagnosis will be “squamous cell carcinoma, well differentiated, without evidence of invasion.” In the minds of many dermatology providers, this diagnosis demands excision—but a KA lesion completely removed by shave biopsy is considered cured.
Histologic examination of these lesions is not always as straightforward as in this case. KAs can be poorly differentiated or demonstrate focal areas of invasion, which justifies excision with margins.
TAKE-HOME LEARNING POINTS
- Keratoacanthoma (KA) is an extremely common low-grade squamous cell carcinoma most often seen on directly sun-exposed skin (eg, hands, arms, face, ears) of older, sun-damaged patients.
- KA typically manifests as a round to oval, dome-like, firm nodule, often with a central keratotic core and a history of rapid growth.
- It’s important to remove these lesions in one piece (eg, by deep shave biopsy) because identification is based on architecture and cellular composition.
- The pathology report will show a well-differentiated squamous cell carcinoma with architecture consistent with KA.
- Although some believe that excision is necessary, a deep shave biopsy performed with clear margins is adequate treatment.