Republican presidential candidate Sen. John McCain has a 6 percent chance of dying of the skin cancer melanoma in each of the next two years, says a doctor who specializes in the design of medical trials.

McCain, 72, has battled melanoma four times, most recently in 2002. After his campaign released 1,200 pages of his medical records in May, his doctor said he had less than a 10 percent chance of the melanoma recurring.

Now, in a letter to the medical journal The Lancet, internist John Alam explains his analysis of those records, based on a predictive model for 10-year survival in melanoma patients. Alam is a biotech consultant in Massachusetts who's contributed money to the Democratic Party and its presidential nominee, Barack Obama.

The lesion doctors removed from McCain's left temple in 2000 was 2.2 millimeters thick, making it high risk, and it wasn't on an extremity — another risk factor. Two more strikes against McCain, according to the model: He's male and was older than 60 when the cancer occurred. All of those factors made his chance of surviving the melanoma just 24 percent when he was diagnosed.

Men with melanomas of the thickness of the one McCain had face an increased risk of dying of the cancer for 15 years after they're diagnosed, according to Alam's letter. That risk is highest seven years after the diagnosis, he writes, and it decreases slightly over the next eight years. That would give McCain a 12 percent chance of dying over the next two years from the disease, which is the deadliest form of skin cancer, he says.

But McCain's risk is cut in half, Alam writes, because biopsies of his lymph nodes were negative, meaning the cancer hadn't spread. "His prognosis should be better than for the overall population" in the prognostic model, Alam concludes. "If we assume that this trend is maintained long term, McCain's mortality risk due to melanoma is better but not eliminated, remaining at 6 percent per year."

A McCain spokeswoman, Jill Hazelbaker, disputed Alam's analysis. "This study is absurd," Hazelbaker said in an email. She cited comments made by McCain's doctors after the release of his medical records in May, characterizing him as being in "excellent health."

(Image of John McCain/U.S. Senate)