This evidence summary covers basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) of the skin, and the related noninvasive lesion actinic keratosis (viewed by some pathologists as a variant of in situ SCC ). Although BCC and SCC are by far the most frequent types of nonmelanoma skin cancers, approximately 82 types of skin malignancies, with a wide range of clinical behaviors, fall into the category of nonmelanoma skin cancer. Other types of malignant disease of the skin include the following:
The PDQ editorial boards use a ranking system of levels of evidence to help the reader judge the strength of evidence linked to the reported results of a therapeutic strategy. For any given therapy, results of prevention and treatment studies can be ranked on each of the following two scales:
Strength of the study design.
Strength of the endpoints.
Together, the two rankings provide a measure of the overall level of evidence. Screening studies are ranked on strength of study design alone...
BCC and SCC are both of epithelial origin. They are usually diagnosed on the basis of routine histopathology obtained from a shave, punch, or fusiform excisional biopsy.
Basal Cell Carcinoma
BCC is at least three times more common than SCC in nonimmunocompromised patients. It usually occurs on sun-exposed areas of skin, and the nose is the most frequent site. Although there are many different clinical presentations for BCC, the most characteristic type is the asymptomatic nodular or nodular ulcerative lesion that is elevated from the surrounding skin, has a pearly quality, and contains telangiectatic vessels.
BCC has a tendency to be locally destructive. High-risk areas for tumor recurrence after initial treatment include the central face (e.g., periorbital region, eyelids, nasolabial fold, or nose-cheek angle), postauricular region, pinna, ear canal, forehead, and scalp. A specific subtype of BCC is the morpheaform type. This subtype typically appears as a scar-like, firm plaque. Because of indistinct clinical tumor margins, the morpheaform type is difficult to treat adequately with traditional treatments.
BCCs are composed of nonkeratinizing cells derived from the basal cell layer of the epidermis. They are slow growing and rarely metastasize. However, they can result in serious deforming damage locally if left untreated or if local recurrences cannot be completely excised. BCCs often have a characteristic mutation in the patched 1 tumor suppressor gene (PTCH1), although the mechanism of carcinogenesis is not clear.