Persons with Parkinson disease (PD) have a lower than expected prevalence of most cancers, but melanoma is an exception. Several studies have found an elevated risk for malignant melanoma in PD patients. A reciprocal increased risk for PD has been reported in melanoma patients and their first-degree relatives, suggesting a common genetic or environmental link. Researchers used the Utah Cancer Registry and the Utah Population Database, which contains birth, death, and family relationship data of more than 2 million individuals, dating back in some instances 15 generations, to assess associations between PD and cancer subtypes.
Among 388,221 individuals with a recorded cause of death and at least three generations of genealogic data, 2998 had PD as a cause of death, and 48 of these had melanoma, versus an expected rate of 24.6 (relative risk, 1.95; 95% confidence interval, 1.44–2.59). Statistically significant excess risk for melanoma was found in the first- and second-degree relatives of those with PD-related deaths. Among 7841 individuals with a melanoma diagnosis and at least three generations of genealogy, the researchers found significantly increased risk for PD-related death in the melanoma cases (RR, 1.65; 95% CI, 1.22–2.19) and in their first-, second-, and third-degree relatives. Prostate cancer was the only other cancer observed in excess in those with PD-related death. Among those with PD-related deaths, men had significantly fewer than expected lung, pancreas, and stomach cancers, and colon cancers were significantly decreased in women. The authors conclude that the findings in this study strongly support the hypothesis of a common genetic link between PD and melanoma.