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Sunlight and melanoma: doctors offer differing views on controversial topic

Posted by D3forU on June 26, 2010

Sunlight and melanoma: doctors offer differing views on controversial topic.

(Special Report) Dermatology Times May , 2008 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.

Q: What is the cause of melanoma?

A: Dr. Ackerman: “I think that melanoma is genetically determined, and that the sun is not responsible for it. Sunscreens don’t prevent melanoma, and the sun itself does not cause melanoma.”

A: 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 I sun exposure play a role in the progression of this disease?

A: Dr. Ackerman: “The sun plays no role at all in initiating the disease. When melanoma occurs in Asians and Africans, it occurs on the soles, the palms, the nail unit and the mucous membranes. It is obvious that melanoma in Asians and African s is not induced by the sun. When the sun truly is responsible for lesions in skin of any color, there are two principles involved that are inviolate: The lesions only occur on sun-exposed sites and are multiple. There are several examples such as freckles, solar lentigines and solar keratoses. But when you look at melanoma, even in Caucasians. it occurs mostly on covered sites, not sun-exposed sites. In 90-plus percent of cases, melanoma is solitary.”

A: Dr. Spencer: “We are dependent on epidemiological studies for the data, and the epidemiological studies do suggest that early and intense exposure plays the great 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.”

A: 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 on e 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 sunexposed 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.”

A: 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.”

Q: Why has the incidence of melanoma increased so dramatically in the past two decades?

A: Dr. Ackerman: “There has been no increase in the incidence of melanoma. An indication of that are the most recent figures from the American Cancer Society. We have far better surveillance and far better criteria clinically and histopathologically for diagnosis of melanoma. There has never been a true epidemic of a malignant neoplasm, and melanoma is no exception.”

A: Dr. Spencer: “There are two explanations. One explanation is that it’s overdiagnosed. The literature does not support that view. The other explanation is that susceptible populations are more exposed to ultraviolet light. In decades past, exposure to ultraviolet light was limited. Now people go to Jamaica or Hawaii for a vacation during winter break. They often burn their skin while on vacation.”

Q: Do severely dysplastic nevi progress to melanoma?

A: Dr. Ackerman: “The mantra at the Clark school is that the dysplastic nevus is the greatest risk factor for melanoma. How can that be if the sun is the cause of it? Most melanomas in Caucasians (85 percent) do not begin in association with a nevus of any kind. Moreover, the so-called dysplastic nevus actually is several different kinds of nevi.”

A: Dr. Spencer: “Dysplastic nevi are a marker of the high-risk individual. but I don’t think the evidence is there that they are literal precursors of melanoma. The kind of person who makes dysplastic nevi is the kind of person who makes melanoma, but dysplastic nevi are not pre-melanomas.”

Q: Do you believe sunlight exposure is necessary for vitamin D production, or can it be obtained more safely from multivitamin tablets?

A: Dr. Ackerman: “I think the best way to get vitamin D is through sun exposure. Vitamin D plays a role in immune responses and in prevention of cancer. It may prove to be that vitamin D that one gets through the sun is really crucial for a healthy life. I can’t believe that the artificial (multi-vitamin) is better than natural. If you burn, stay out of the sun. If you tan, a certain amount of daily sun is advantageous to your health.”

A: Dr. Spencer: “You can easily get the recommended daily allowance of vitamin D with a normal diet. Some people feel mega doses of vitamin D improve health. It would be hard to get that from your diet. The answer is to take a vitamin pill. You don’t need to jeopardize your health with intentional tanning to get vitamin D.”

BY LOUISE GAGNON STAFF CORRESPONDENT

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