Solar Exposure, Hive and Risk of Melanoma in Botswana: a Case-control Study

Malignant melanoma is the cancer of the skin in which melanocytes develop into malignant cells.It accounts for about 4% of all skin cancers but responsible for 80% of cancer related deaths in the US. Malignant melanoma is the 6th common cancers among women and 5th among men in the United States Of America it usually detected or diagnosed at adult stage with a median age at the time of diagnosis being 58 years and only 0.9% of the cases before age of 20(1).

Its incidence increased rapidly in the 1970s at about 6% per year. It has been estimated that the annual incidence increase is about 3-7%. The increase in incidence rate has been attributed to screening and early detection of malignant melanoma and awareness (2).

This type of skin cancer is more common amongst the Caucasian population when compared to the black people. People with light skin are at increased risk of developing melanoma, about 17-25 times (1). Melanoma is reported to be more extremely rare the blacks and most cases were acral lentiginous subtype (3, 4). Africans tend to have protection form the carcinogenic effects of UV radiation than Caucasians due to greater levels of melanin. The most common sites on which acral lentiginous melanomas develop in Africans and African–Americans are nail beds, soles and palms. In a retrospective analysis of melanoma in South Africans of mixed ancestry showed histological type and anatomic distribution that is characteristic of black populations, yet the 5-year survival rate in these patients was similar to that seen in white populations (5). Annual increase in the incidence rate of melanoma has been estimated to be 3–7% per year Caucasians (6).

In most cases malignant melanoma is diagnosed at stage 3 or above, with a median survival of 6-9 months and 5 year survival rate of less than 5% (7, 8).

The major predisposing factors are family history, exposure to UV radiation, either intermittent or chronic exposure, fair skin, history of melanoma. In a study done by Radespiel-Tröger, M., et al, confirmed that there is an increased risk of melanoma in outdoor workers (9). Outdoor workers had more risk behavior with similar constitutional skin cancer risk factors: more UV exposure (both occupational and leisure) and less sunscreen use and lower health literacy). This results in higher exposure, more photo damage and an increased risk of developing Basal Cell Carcinoma and Squamous Cell Carcinoma (10). The high levels of sun exposure may be associated with with skin cancers in people who work outdoor, together with insufficient use and practice of sun protective measures when working outside(11). A large number of people are exposed to varying levels of solar radiation at the workplace. In a study using the CAREX (carcinogen exposure) database designed to provide selected exposure data and documented estimates of the number of workers exposed to carcinogen by country, reported that the most common occupational exposure to carcinogens in the EU countries was solar radiation (12).