Basal Cell Carcinoma
Basal cell carcinoma (BCC) is the most common malignancy in people of European descent, with an associated lifetime risk of 30%. While exposure to ultraviolet radiation (UV) is the risk factor most closely linked to the development of BCC, other environmental factors (such as ionizing radiation, chronic arsenic ingestion, and immunosuppression) and genetic factors (such as family history, skin type, and genetic syndromes) also potentially contribute to carcinogenesis. In contrast to melanoma, metastatic spread of BCC is very rare and typically arises from large tumors that have evaded medical treatment for extended periods of time. BCCs can invade tissue locally or regionally, sometimes following along nerves. A tendency for superficial necrosis has resulted in the name "rodent ulcer." With early detection, the prognosis for BCC is excellent.
Risk Factors for Basal Cell Carcinoma
Sun exposure is the major known environmental factor associated with the development of skin cancer of all types. There are different patterns of sun exposure associated with each major type of skin cancer (BCC, squamous cell carcinoma [SCC], and melanoma).
While there is no standard measure, sun exposure can be generally classified as intermittent or chronic, and the effects may be considered acute or cumulative. Intermittent sun exposure is obtained sporadically, usually during recreational activities, and particularly by indoor workers who have only weekends or vacations to be outdoors and whose skin has not adapted to the sun. Chronic sun exposure is incurred by consistent, repetitive sun exposure, during outdoor work or recreation. Acute sun exposure is obtained over a short time period on skin that has not adapted to the sun. Depending on the time of day and a person's skin type, acute sun exposure may result in sunburn. In epidemiology studies, sunburn is usually defined as burn with pain and/or blistering that lasts for 2 or more days. Cumulative sun exposure is the additive amount of sun exposure that one receives over a lifetime. Cumulative sun exposure may reflect the additive effects of intermittent sun exposure, or chronic sun exposure, or both.
Different patterns of sun exposure appear to lead to different types of skin cancer among susceptible individuals. Intermittent sun exposure seems to be the most important risk factor for melanoma. BCC appears to share some risk factors with melanoma.[2,3] Some BCCs may be caused by chronic sun exposure, but a large portion (one-third or more) is apparently caused by intermittent sun exposure, similar to that implicated in melanoma. Occupational exposures are associated with SCC risk and recreational exposures with BCC risk. This exposure-response pattern is consistent with the results from a randomized trial of sunscreen efficacy that found statistically significant protection for the development of squamous cell carcinoma but no evidence at all for protection from the development of BCC. It is unlikely that such a trial could be carried out for melanoma because of a lack of statistical power. Therefore, the similarities between BCC and melanoma are all the more critical to understand.