Basal cell carcinoma

Abstract

The common occurrence of basal cell carcinoma, especially in younger populations, has made it a major public health concern. It is the commonest malignancy affecting humans and is largely preventable. These facts have made it the focus of national attention and public education campaigns. Convincing epidemiologic data incriminate ultraviolet B (UVB) as a major etiologic factor, but there is also sufficient evidence that it is not the sole causative agent. Other agents implicated in the cause of basal cell cancers include long-term psoralen plus ultraviolet A (PUVA) therapy, grenz radiation, X-radiation, chronic arsenicism, preexisting lesions such as sebaceous nevus of Jadassohn and linear basal cell nevus, and genetic diseases such as xeroderma pigmentosum and nevoid basal cell carcinoma syndrome. Despite the fact that UVB has been recognized as a cause for several years, the pathophysiology of UVB-induced basal cell cancers has not been completely defined as yet. Other factors lead to the formation of basal cell cancers by different mechanisms, the pathophysiology of some being poorly understood. Recognition of the causes of basal cell cancers has led to the development of preventive measures such as photoprotection by avoidance of excessive sun exposure and use of sunscreens, limited use of grenz ray and x-ray therapy of the skin, monitoring of well water for its arsenic content, and prophylactic excision of nevus sebaceous when such a lesion is detected. Awareness of the increasing incidence has led to the development of screening programs for early detection of lesions also. Understanding of the biology of basal cell cancers continues to unfold with continuing investigation. Studies suggest that collagenase, derived from tumor stromal fibroblasts, plays a role in creating a path for tumor invasion by digesting collagen in the surrounding dermis. Fibronectin formed by tumor cells may be involved in tumor cell migration as well. Transplantation studies in animals have shown that immunologic phenomena play an important role in the biology of basal cell cancers. Human basal cell carcinoma has been recently transplanted successfully to immunosuppressed athymic mice. The human host allows growth of the cancer due to ultraviolet radiation (UVR)-induced immunosuppression. Immunologic abnormalities have been documented in patients with basal cell cancers. Immunologic deterioration may be a factor in the rare instance of metastatic basal cell cancer. Cognizance of the various common and uncommon clinical appearances of these neoplasms is important so that they can be recognized and treated effectively. The most common presentation is as a pearly papule or nodule with surface telangiectasias on a sun-exposed surface; other presentations include the pigmented, morpheaform, superficial, and fibroepithelioma of Pinkus types. Basal cell cancers may also be encountered on sun-protected areas. Familiarity with the logic behavior of the various types allows selection of the appropriate therapeutic modality. The histologic types of clinical import are the nodular, superficial, morpheaform, adenoid, and metatypical lesions. The latter three types invade local tissues more aggressively and consequently are best treated with Mohs surgery to ensure complete extirpation. Histologic confirmation of the diagnosis and definition of tumor type should be obtained prior to therapy. The six usual approaches for treatment are curettage and electrodesiccation, excision, cryosurgery, radiation therapy, topical chemotherapy, and Mohs micrographic surgery. The retinoids, etretinate and isotretinoin, have been useful in controlling the rate of appearance of basal cell cancers in patients with multiple basal cell cancers due to extensive sun exposure, xeroderma pigmentosum, and nevoid basal cell carcinoma syndrome. However, maintenance therapy is necessary for continued control. Systemic chemotherapy may be useful for reducing the size of inoperable tumors so that may become amenable to surgical resection, but this is seldom required. Indefinite follow-up and patient education are essential elements of management of basal cell carcinomas.