Melanoma on the Rise, or Is It Just Diagnoses?
By NICHOLAS BAKALAR
NYT  September 28, 2009 http://www.nytimes.com/2009/09/29/health/29mela.html?_r=2 
In recent years there has been a sharp rise in reported cases of malignant melanoma, the deadliest form of skin cancer. But a British study has found evidence that the epidemic may be due at least in part to “diagnostic drift,” a growing tendency to identify and treat benign lesions as malignant cancers. The findings may raise the temperature in an already-heated controversy.
The study, published in the September issue of The British Journal of Dermatology, examined a cancer registry with 3,971 cases of melanoma and found that incidence increased 48 percent from 1991 to 2004, similar to the 44 percent increase reported by the Centers for Disease Control and Prevention over the same period for American whites. The disease is almost 20 times as common in whites as in blacks.
But the British researchers found something odd in the data: almost all of the increase was in diagnoses of the earliest stage of the disease, where it is difficult, and sometimes impossible, to tell a malignant lesion from a melanocytic nevus, a type of benign mole. There was no change in the combined incidence of the later stages of the disease, and mortality increased only slightly.
One possible explanation is that dermatologists and pathologists are finding cases earlier, treating them, and preventing more serious disease from developing. But melanoma is commonly diagnosed at various stages of severity, and if its incidence were truly increasing, the authors write, there would be increases found in all stages of the illness, not just the earliest.
“We think that in borderline cases dermatologists and pathologists are erring on the side of caution,” said the lead author, Dr. Nick J. Levell, a dermatologist at Norfolk and Norwich University Hospital in England. “Over time, the criterion for what is a cancer gradually moves.”
Experts not involved in the study expressed widely varying opinions.
“Every study over the past 10 years has shown that the absolute number of melanomas is rising,” said Dr. Darrell S. Rigel, a professor of dermatology at New York University. The death rate from melanoma has also been going up, Dr. Rigel said, but so has the survival rate. In other words, while more people are getting the disease and dying from it, early identification and treatment has simultaneously allowed more people to survive.
But if this were so, Dr. Levell said, “there would have to have been a coincidence of a large increase of just Stage 1 melanoma which had been almost exactly matched in both time and magnitude by a large improvement in therapeutic effect.” He finds this “improbable.”
Marianne Berwick, a professor at the University of New Mexico who has widely published on the epidemiology of melanoma, said the study was controversial but convincing. “A lot of dermatologists will argue that they’re getting better at diagnosing melanoma, but I don’t think that’s very likely,” Dr. Berwick said. “They’re taking a lesion that would not be diagnosed as melanoma 20 years ago and calling it melanoma.”
The issue is further complicated by the role of sun exposure. Dr. Julide Tok Celebi, an associate professor of dermatology at Columbia, strongly disagreed with the study’s conclusions. The increase in melanoma is real, she said, and “the only logical explanation is environmental exposure.” She added that these days people were being exposed to “significantly greater” amounts of ultraviolet radiation.
But Dr. Levell said sun exposure, even though it had well-established risks, could not explain his findings. “Squamous and basal cell carcinomas are no doubt caused by sunlight,” he said, “and those increases are concentrated on the face and neck.” But the diagnoses of melanoma in the registry were mostly on the back, trunk and limbs, areas not consistently exposed to the sun. This means that exposure to sunlight cannot explain the increased number of lesions reported as malignant, he said.
Dr. Levell acknowledged that while his research suggested that diagnostic error explained the melanoma epidemic, it did not provide proof. What is needed, he said, is a randomized study.
“Look at cases 15 years ago, look at cases today,” he said. “Jumble them up and analyze them in a blind study to find out if it’s true. No one has managed to do this yet.”