Although no specific etiology is apparent in most individual cases of carcinoma of the skin, a number of intrinsic or extrinsic factors are thought to play a role in the over-all picture. Probably the most commonly encountered situation is that of an individual with a carcinoma-prone complexion of the type to be described below who gives a long history of exposure to the sun and elements.

Complexion Or Type Of Skin

A person's complexion or skin type is the end result of such a host of complex factors, including race, heredity, genetic constitution, etc., that it is impossible to be at all precise about the significance or nature of this as a predisposing factor. However, the following statement can be made-skin cancer is particularly common among those individuals whose skin is light or sandy in color, is soft in texture, and has a tendency toward freckling and burning rather than tanning on exposure to the sun. Such persons are likely to have blue or other lightly pigmented eyes. Thus it is apparent that persons with racial or national origin in the northern or certain middle European latitudes are particularly vulnerable to skin cancer provided there is sufficient exposure to the sun. Conversely, those with darker skin and eyes from the more southerly latitudes display a particularly low incidence of skin cancer even though exposure to solar radiation is generally much higher.

Sunlight

The assumption that skin carcinoma is related to exposure to the sun is based on several observations. For example:

1. The skin of the patient with squamous cell or basal cell cancer often shows the effects of long-term, heavy exposure to sunlight.

2. The majority of all skin carcinomas occur on the exposed surfaces of the body (e.g., head and neck region, dorsum of the hands, etc.)-those areas accessible to the sun's rays.

3. There is a striking discrepancy in the incidence of such cancer in various geographic areas, the principal difference between the regions apparently being the amount and intensity of exposure to sunlight encountered. Thus, in some parts of the southern United States skin carcinoma is 5 to 10 times as common as in the north.

4. Skin carcinoma often occurs in several different sites on the same individual within a relatively short time period. This usually is a reflection of the exposure of a person to a diffusely applied carcinogenic agent, such as, in this case, sunlight.

It is further assumed that the most important factor contributing to the carcinogenic effect of sunlight is the ultraviolet rays since they are known to produce cancer by themselves in the experimental animal. It is apparent, however, that many other factors, including heat, wind, rain, etc., act in concert to produce the familiar "weather-beaten" countenance of the "outdoor" man or woman.

Radiation

Exposure to ionizing radiation is a well-documented cause of skin cancer. The skin of the pioneers in the field of radiology who unwittingly exposed themselves to large doses and subsequently developed multiple, recurrent cancers has borne adequate testimony to this. Similarly, the occurrence of comparable malignant lesions of the face in areas radiated because of acne, hirsutism, etc. is further evidence of the causal relationship between the two.

Arsenic

Skin cancer related to the ingestion of arsenic is one of the oldest of the known occupational cancers. Less commonly it has been ascribed to arsenic prescribed with medicinal intent. More recently, attempts have been made to link some cases of skin cancer to exposure to arsenic-containing insecticides, herbicides, etc.-with inconclusive results. Cancers caused by arsenic have an unusual prediction for the palms of the hands and soles of the feet.

Burn Scan

A number of cases of carcinoma have been reported at the site of burns sustained many years previously. This appears to be particularly true for thermal burns as opposed to electrical, chemical, or other bums, but this may be true only because thermal burns are so much more common.

Tar, pitch, soot, oils, and other petroleum products

Skin cancer caused by exposure to these agents is almost exclusively an occupational problem. It usually requires many years of contact, and the exposure generally must be fairly intense and intimate. The lesions occur wherever the exposure is greatest. For example, carcinoma of the skin of the thighs or scrotum may result from longstanding contact with pants and underclothes impregnated with any of the above carcinogenic agents. Poor local hygiene obviously plays a strong supporting role in these instances.