They hypothesized that immunosuppressive medications may increase the risk of melanoma by "down-regulation of the tumor surveillance mechanisms, increased susceptibility to infection with oncogenic viruses such as melanoma-associated retroviruses, or through direct pharmacologic effects of medications on DNA metabolism. Although thiopurine analogs have been associated with an increased risk of nonmelanoma skin cancers, our pooled analysis did not suggest an increased risk of melanoma, albeit there were a limited number of studies."
Dr. Singh and his associates acknowledged certain limitations of the analysis, including the potential for misclassification bias in the included studies and the fact that studies "did not adjust for known risk factors for melanoma, including personal history of nonmelanoma skin cancers, family history of melanoma, or sun exposure."
For the meta-analysis, one author, Dr. Edward V. Loftus, disclosed that he has consulted for and has received research support from Janssen Biotech, Abbott Laboratories, and UCB Pharma. The others had no relevant conflicts to disclose.