Basal Cell Carcinoma: Variants and Challenges
Basal cell carcinoma (BCC) is the most common cutaneous carcinoma. The annual incidence of BCC in the United States is approximately 1,100,000 cases, which outnumbers the next most prevalent carcinoma (squamous cell carcinoma) by a factor of four and melanoma by a factor of 20. Common to the aforementioned neoplasms, the etiology of BCC is most closely related to excessive ultraviolet exposure and, accordingly, is most commonly diagnosed in the elderly on the exposed cutaneous surfaces, especially in residents of sunny geographic locales. Exceptions to this rule are rare yet can be observed in certain genetic syndromes that may predispose to multiple BCC’s occurring in exceptional anatomic locations and age ranges. These syndromes include xeroderma pigmentosa, the Basex and Basal Cell Nevus syndromes. It is in the latter syndromes that the pathogenesis has been discerned and relates to the development of sporadic forms of this disease as well. The pathogenesis involves mutations in the human homologue of the Drosophila gene patched (PTCH1) where it functions as a tumor suppressor gene. Loss of this gene or its function along with acquired (ultraviolet-induced) defects in the p53 gene and the apoptosis-regulating gene BAX has also been implicated in the pathogenesis.