Basal cell carcinoma is the most common form of skin cancer, predominantly affecting the head and neck, and can usually be diagnosed clinically.

• Metastasis of basal cell carcinoma is rare, but localized tissue invasion and destruction can lead to morbidity.

• Risk factors for basal cell carcinoma include tendency to freckle, degree of sun exposure, excessive tanning bed use, and smoking.

• The incidence of basal cell carcinoma increases markedly after age 40 years; however, the incidence in younger persons is rising, possibly from increased sun exposure.

Excisional surgery is considered likely to be effective in treating basal cell carcinoma.

• Similar treatment response rates one year after treatment have been reported for excisional surgery compared with photodynamic therapy and curettage plus cryotherapy.

• Excisional surgery is associated with fewer adverse effects compared with photo-dynamic therapy and curettage plus cryotherapy, and it seems to be associated with improved cosmetic results compared with curettage plus cryotherapy one year after treatment.

• We cannot compare the effectiveness of surgical excision with Mohs' micrographic surgery in treating recurrent basal cell carcinoma, but excisional surgery seems to be associated with more adverse effects compared with Mohs' micrographic surgery.

Cryotherapy with or without curettage, photodynamic therapy, and curettage and cautery/electrodesiccation may be effective treatments for basal cell carcinoma in the short-term (up to one year after treatment).

• Cryotherapy alone seems to be as effective as photodynamic therapy for superficial and nodular basal cell carcinomas, but photodynamic therapy may produce better cosmetic results compared with cryotherapy alone.

• We do not know how cryotherapy with curettage compares with photodynamic therapy or cryotherapy alone.

• Two treatments with photodynamic therapy performed one week apart with delta-aminolevulinic acid may be more effective than single treatments in the short-term.

• There seems to be no difference in effectiveness between delta-aminolevulinic acid using a broadband halogen light source and delta-aminolevulinic acid using a laser light source.

Imiquimod 5% cream may be beneficial for the treatment of superficial and nodular basal cell carcinomas compared with placebo in the short-term (within six months after starting treatment).

• More frequent use of imiquimod 5% seems to improve response rates compared with less frequent regimens, but is also associated with increased adverse effects.

We do not know whether fluorouracil is effective in the short-term treatment of basal cell carcinoma.

Excisional surgery, cryotherapy alone, photodynamic therapy, and curettage and cautery/electrodesiccation are thought to be beneficial in preventing long-term recurrence of basal cell carcinoma.

We do not know whether imiquimod 5% and fluorouracil are effective in preventing basal cell carcinoma recurrence in the longer term (at or beyond two years of treatment).

Definition

Basal cell carcinoma is the most common cancer in humans. It is a slow-growing, locally invasive, malignant epidermal skin tumor that mainly affects white persons. Although metastasis is rare, basal cell carcinoma can cause morbidity by local tissue invasion and destruction, particularly on the head and neck. The clinical appearance and morphology are diverse, including nodular, cystic, ulcerated (rodent ulcer), superficial, morpheic (sclerosing), keratotic, and pigmented variants. Most basal cell carcinomas (85 percent) develop on the head and neck.

Diagnosis: The diagnosis is usually made clinically. A biopsy is performed for histologic diagnosis when there is doubt about clinical diagnosis, and when persons are referred for specialized forms of treatment.

Incidence

The reported incidence of basal cell carcinoma varies in the literature. In 1995 in Australia, the incidence was reported to be 788 per 100,000 population per year; and in 1990 in the United States, it was reported to be 146 per 100,000 population per year. A Dutch study reported an incidence of 200 per 100,000 population per year, whereas the incidence in the United Kingdom is reported to be lower, at about 100 per 100,000 population per year. Because of incomplete registration of cases, some of these estimates may be low. The incidence of basal cell carcinoma increases markedly after 40 years of age, and the incidence in younger persons is rising, possibly as a result of increased sun exposure.

Etiology/Risk Factors

The reported risk factors for developing basal cell carcinoma include fair skin, tendency to freckle, degree of sun exposure, excessive tanning bed use, smoking, radiotherapy, phototherapy, male sex, and a genetic predisposition. Although cumulative lifetime sun exposure is a major risk factor, on its own, it does not accurately predict the frequency of basal cell carcinoma development at a particular site. Other contributory factors are skin phototype (e.g., Fitzpatrick I and II), number of lifetime visits to tanning beds, number of pack-years of cigarette smoking, and number of blistering sunburns. Immunosuppressed patients are also at increased risk of nonmelanoma skin cancer, including basal cell carcinoma. The risk increases with duration of immunosuppression, and about 16 percent of persons with renal transplants develop basal cell carcinoma—a 10-fold increased risk compared with the general population. The autosomal dominant condition nevoid basal cell carcinoma syndrome (Gorlin syndrome) is characterized by the occurrence of multiple basal cell carcinomas and developmental abnormalities.

Prognosis

The following factors can affect prognosis: tumor size, site, type, growth pattern/histologic subtype, failure of previous treatment (recurrence), and immunosuppression. Basal cell carcinomas that are in close proximity to important body structures can potentially increase morbidity as a result of local tissue invasion or recurrence. Therefore, basal cell carcinomas can be categorized based on location: high risk (nose, nasal-labial fold, eyelids and periorbital areas, lips, chin, and ears); medium risk (scalp, forehead, pre- and postauricular areas, and malar areas); and low risk (neck, trunk, and extremities). Histologically, micronodular, infiltrative, morpheic, and basosquamous types of basal cell carcinoma are classified as high risk.

Distant metastases are rare. Although some basal cell carcinomas tend to infiltrate tissues in a three-dimensional manner, growth is usually localized to the area of origin. However, if left untreated, basal cell carcinoma can cause extensive tissue destruction with infiltration in deeper tissues, such as the bone and brain. Basal cell carcinomas may remain small for years with little tendency to grow, grow rapidly, or proceed by successive spurts of extension of tumor and partial regression. Therefore, the clinical course of basal cell carcinoma is unpredictable.