Doctors offer different views on sunlight and melanoma

May 1, 2008

Dermatology Times asks two leading dermatologists whether sun exposure triggers melanoma.

Key Points

National report - Dermatology Times asks two leading dermatologists whether sun exposure triggers melanoma.

Bernard Ackerman, M.D., director emeritus of the Ackerman Academy of Dermatopathology in New York, and a professor of dermatology and pathology at Downstate University Medical Center in Brooklyn, N.Y., has challenged prevailing views about the relationship between sunlight and the development of melanoma.

James Spencer, M.D., a faculty member at Mount Sinai Hospital in New York who currently practices dermatology in Florida, has been actively involved in sun awareness campaigns and campaigns against indoor tanning, with the support of the American Academy of Dermatology.

Dr. Spencer: "The best evidence is that melanoma is a result of sunlight exposure. The epidemiologic evidence is strong, including the observation of a dramatic increase in incidence as fair-skinned, sun-sensitive peoples move closer to the equator. Certainly, the occurrence of melanoma in patients with xeroderma pigmentosum is compelling. These patients cannot repair ultraviolet-induced DNA damage and have a remarkable increase in skin cancer incidence, including melanoma."

Q. Does early or intense sun exposure play a role in the progression of this disease?

Dr. Spencer: "We are dependent on epidemiological studies for the data, and the epidemiological studies do suggest that early and intense exposure plays the greatest role. But the studies also suggest that adult exposure plays a role."

Q. Can tanning booth exposure promote the development of melanoma?

A. Dr. Ackerman: "There is no compelling evidence that sun tan parlors have induced a single melanoma. The industry should be controlled if, in fact, the industry induces cancers, but that should be predicated on evidence and not on accusation."

Dr. Spencer: "We don't have direct experimental evidence. The biggest and most recent studies that compare subjects to age-matched controls suggest that indoor tanning is an independent risk factor for the development of melanoma. No study has ever shown indoor tanners get less melanoma, as the vitamin D advocates would suggest."

Q. Why is the incidence of melanoma wildly different in various parts of the world, with the highest incidence in sunny climates?

A. Dr. Ackerman: "This comes from epidemiological data. Some studies have shown that the closer to the equator, the higher the incidence of melanoma. That doesn't mean the sun is responsible for the higher incidence. The Irish in Australia have a high incidence of melanoma, but so do the Irish in Ireland."

Dr. Spencer: "If you compare people of English heritage in Australia to people of English heritage in England, the two groups are relatively genetically homogeneous. But Australia has the highest melanoma rate in the world. That is one of the most compelling arguments that sun exposure causes melanoma."

Q. Why does the location of the average melanoma differ from that of two sun-induced tumors, BCC and SCC, namely on the head and neck region?

A. Dr. Ackerman: "Solar keratoses occur only on sun-exposed sites. It is established that the sun is the cause of solar keratoses. The opposite is true for melanoma. As for basal cell carcinoma, the evidence is far from compelling that the sun is the major cause of it."

Dr. Spencer: "One explanation is that it's a result of intermittent highest-intensity exposure. You are more likely to get sunburned on your back. You don't expose your back much, and then men take their shirts off at the beach, and that is where the burn occurs. The back has the highest incidence of melanoma in men; the legs, in women. Another possibility is that the effects of the sun are systemic and not limited to areas of direct exposure. For example, ultraviolet light-inducing immunosuppression is systemic. Lastly, I think it will turn out that melanoma, like most things, is multifactorial, but ultraviolet radiation seems to be the major factor."