Theories and Facts on Melanoma

Theories and Facts on Melanoma

Lately, many articles have been written that attempt to explain the increase in melanoma. Many of these articles use negative language to imply that ultraviolet radiation induces melanoma, without actually stating that it does. This writing style often leaves the reader with the wrong impression. As a salon owner, you need to know the scientific truth. Below are three examples of seemingly credible "scientific" theories, each followed by a deeper analysis of scientific fact.

Sunscreen Use Increases the Incidence of Melanoma

Theory: In 1993, the Garland brothers of San Diego proposed that sunscreens are responsible for the increase in melanoma. They examined large populations and reported that the rise in melanoma correlated with a rise in sunscreen sales. The Garland's offered two possibilities for the correlation in sunscreen sales and increased melanoma.

First, they suggested that sunscreen filters the UVB rays, but still allows the UVA rays to penetrate into the skin. Their suggestion indicates that UVA severely damages the skin in ways that have not been discovered.

Second, the Garland's suggested that sunscreen use reduces the amount of UVB reaching the skin that is necessary for vitamin D production. The lack of vitamin D might lead to the increased levels of melanoma.

Fact: Considering existing and new data, skin cancers and melanoma probably take about 15 to 20 years to develop. If the increased sales of sunscreen were responsible for the increase in melanoma, we would expect to see a delay of about 15 years between the increase in sunscreen sales and the increase in melanoma. However, this is not the case.

During the 1995 Biological Effects of Light Symposium, Dr. Fred Urbach stated that the incidence of melanoma has been doubling consistently every 10 years since the 1930s, according to the Connecticut Registry. This would indicate that whatever is causing the increase in melanoma first began around 1915, or earlier, and sunscreens began in the 1940s. Clearly, sunscreens had no effect on melanoma development in the 1930s.

Vitamin D deficiency has not been associated with increased incidence of melanoma. In the 19th century, children in the inner cities of England suffering from rickets were not reported to have had an increased incidence of melanoma. Rickets results from a severe deficiency in vitamin D. To my knowledge, there has never been any study correlating an increase in melanoma with vitamin D concentration.

Theory: In 1993, a scientific group reported that a common UVB sunscreen, octyl dimethyl p-amino-benzoic acid, caused DNA changes in yeast cells exposed to ultraviolet radiation. The group offered that this effect could cause similar changes in humans, resulting in melanoma.

Fact: The DNA changes observed in yeast cells have never been observed in human skin. When the sunscreen has been used in laboratory studies, it always has decreased the formation of basal cell and squamous cell cancer. Melanoma, however, never has been induced successfully in laboratory mammals, despite large doses of ultraviolet radiation over long periods of time. Laboratory mammals seem to not suffer from melanoma like humans, therefore, studies on them are not appropriate.

Sun Exposure Increases the Incidence of Melanoma

Theory: Another wide-spread theory is that exposure of the skin to ultraviolet radiation increases the incidence of melanoma in a population.

Fact: This is the essence of a highly contentious issue between the tanning industry and the American Academy of Dermatology. Ultraviolet radiation has been implicated in the development of squamous cell and basal cell carcinoma, but very little evidence supports a correlation between exposure to ultraviolet radiation and an increase in the incidence of melanoma.

As stated above, no one has been able to produce UV-induced melanoma consistently in laboratory mammals. However, two species of fish are remarkably sensitive to melanoma production by visible light as well as by UV radiation. Almost all agree that the results with the fish cannot be extrapolated to humans. Without an appropriate animal model, the scientific community has had to rely on epidemiological studies. (Epidemiological studies gather large amounts of data on a human population and seek correlations within that data.) The studies do not support a direct correlation between sun exposure and melanoma; however, they do indicate that some sort of interaction exists.

First, most studies show that melanoma is more prevalent in higher latitudes, where the sun is less intense. Second, most studies show that indoor workers suffer from more melanoma than outdoor workers. And, third, most studies show that melanoma occurs more frequently on covered areas of the body rather than exposed areas of the body.

No one really understands what all of this means, although one possibility is that excessive intermittent sun exposure may be more likely to induce melanoma than moderate consistent exposure to ultraviolet radiation. The indoor worker who is rarely exposed to the sun, but burns excessively during his two-week vacation is more likely to incur melanoma than the person who works outdoors every day. This logic should lead one to support moderate controlled indoor tanning, tanning that would avoid burning.

If we accept Dr. Urbach's figures that the incidence of melanoma has been doubling every 10 years since the 1930s, then we should ask what has happened to our sun habits that has contributed to this increase. The sun has not significantly increased in intensity, so the only possibility is that Americans have increased their exposure time vastly. However, melanoma occurs more frequently in indoor workers and in Northern latitudes. This suggests that the sun is not at fault, but maybe our exposure patterns are. Again, if excessive intermittent exposure is at fault, moderate controlled tanning is an answer.

Tanning Bed Exposure Causes Melanoma

Theory: Many have tried to link the tanning industry with melanoma, suggesting that the increase in melanoma is due to an increase in popularity of tanning beds. Recent evidence by Dr. Robert Stern indicates that one therapy for psoriasis, PUVA therapy increases the risk for melanoma.

The patient takes a psoralen pill before being exposed to UVA. After more than 15 years of such therapy, the incidence of melanoma is significantly increased. There is no doubt that PUVA therapy induces melanoma. This is the first incidence of a clear and obvious correlation between an act (PUVA therapy) and the induction of melanoma.

Fact: In an article published in LOOKING FIT earlier, I discussed the issues raised by Dr. Stern's finding and concluded that PUVA therapy is not the same as exposure in a tanning bed. Neither psoralens nor UVA has been found to induce melanoma, only the combination. The combination of psoralens and UVA exposure should be avoided. Exposure to UV radiation in tanning beds has not been shown to induce melanoma, and the data from sun exposure would suggest that tanning beds will not induce melanoma in our population.

One physician suggested that the increase in melanoma is not real, that it is due to the increased sensitivity of the public and dermatologists. He argues that physicians remove more moles because they fear melanoma. These are recorded as melanomas when, in fact, they are not. (Differentiating a mole from a melanoma is difficult.) The physician suggests this is the reason why deaths from melanoma are not increasing while the number of melanomas are doubling every 10 years.

What Causes Melanoma?

There are many theories and very few facts on the cause of melanoma. From Dr. Stern's research, we can conclude that PUVA can induce melanoma after 15 years of treatment. We know little else about the cause of melanoma for certain.

My perspective is that a combination of agents causes melanoma. Perhaps the combination is strong sun exposure with some specific type of chemical, as is the case with PUVA therapy. More research in this area is necessary to obtain the answers.