Clive Anderson - AT THE DERMATOLOGIST SKIN CANCER has become the most common malignancy in the United States.
It is felt that the underlying cause of most skin cancers is the accumulated damage to the skin inflicted by years of exposure to the sun. In some cases, there may also be a genetic predisposition to skin cancers. The increased level of melanin in black skin is photoprotective and this seems to account for the reduced frequency with which skin cancers occur in skin of colour.
The most common types of cancers of the skin are:-
Basal cell carcinoma this cancer arises in the lower or basal layer of the skin. It seldom metastasises although it may do so if the cancer invades the lymph or blood vessels. The major mode of spread of the cancer is by local invasion of surrounding tissues. This cancer is the most common skin cancer accounting for 75 per cent of all non-melanoma skin cancers. More than 99 per cent of all basal cell carcinomas occur in whites. These tumours arise most commonly on the face, head or neck. The rarity of this cancer in blacks is explained by the important role played by ultra violet radiation in the development of the tumour and the protective role of black skin.
Squamous cell carcinoma develops in the outer layer of the skin. It is capable of metastasising to other areas of the body if left untreated. It also spreads locally and may cause disfigurement. As with the basal cell carcinoma, excessive sun exposure is a major risk factor. This is the most common malignancy in blacks.
Numerous studies indicate that sun exposure is not a significant factor in the development of this type of cancer in blacks. The lesions tend to develop on non-sun exposed skin. Unfortunately, the squamous cell carcinomas developing on non-sun exposed skin tend to be more serious with a greater potential to spread or metastasise.
When these tumours develop on the sun-exposed areas of black skin, it tends to be on highly-irradiated areas such as the tip of the nose, forehead and lower lip. Squamous cell cancers may develop in scar tissue arising from any chronic process such as burns, chronic leg ulcers or discoid lupus erythematosus. Blacks with squamous cell carcinoma are more likely to die than are whites. This is often because of delayed diagnosis and thus, more advanced disease. It may also be that the cancers arising from scars, burns or ulcers are more aggressive.
Malignant Melanoma fair-skinned people are much more likely to develop a melanoma. Risk factors in black skin are blistering sunburns, albinism, burn scars, pre-existing pigmented lesions and a history of trauma. In black skin, the cancer lesions arise most often on non-sun exposed skin with less pigment such as palms, soles and the area under the nails.
A particularly aggressive type of tumour occurs most commonly on the soles of the feet, the palms and digits and presents as a dark rapidly spreading patch. These lesions have a tendency to spread (metastasise) to the central nervous system, liver, lungs, bone and lymph nodes. The prognosis is often poor.
There is conclusive evidence that UV radiation damages the DNA in the cell leading to mutations and cancers. This may be a two-step process, the UV both initiating and promoting the development of malignancies. UV light appears to harm a mechanism for repairing cell damage. Once the repair system is damaged the cell becomes vulnerable to injury.
In black skin the melanin content of the skin is the first line of defence. It is estimated that melanin confers a Sun Protection Factor (SPF) of 15. This should be supplemented by the application of a sunscreen of at least SPF 15 to the exposed areas (face, arms, neck) on a daily basis. Take note that a sunscreen with SPF 15 blocks 93 per cent of UV from the sun when properly applied. Moving to a product with SPF 30 does not confer twice the protection but an increase of only three per cent more to 96 per cent.
It is important to remember that two types of UV radiation reach the earth UVA and UVB. Both contribute to skin damage skin cancers and photo ageing of the skin. Any sun block used must protect against both UVA and UVB. Skin cancers are easily treated when diagnosed early. Do regular skin self-examinations and have a Dermatologist check any suspicious spots.
Dr. Clive Anderson is a Dermatologist and Venereologist.
