The association between cancer and amyotrophic lateral sclerosis.

Objective: Increasing evidence suggests that some neurodegenerative disorders, such as Parkinson's disease, are inversely related to cancer. Few epidemiologic studies have examined the relationship between cancer and amyotrophic lateral sclerosis (ALS), another major neurodegenerative disease. This study addresses that gap.

Methods: Using data from 16 population-based cancer registries of the Surveillance, Epidemiology, and End Results (SEER) Program of the U.S. National Cancer Institute and death certificates, we followed 2.7 million cancer survivors who were diagnosed between 1973 and 2007, and who survived at least 1 year following cancer diagnosis. The standardized mortality ratio (SMR) of observed to expected ALS deaths in cancer survivors was calculated.

Results: A total of 1,216 ALS deaths were reported among 1 year survivors of cancer over 16.6 million person-years of follow-up. ALS mortality was not significantly associated with the incidence of total cancers [SMR = 1.00 (95 % confidence interval (CI), 0.95-1.06)]. There was, however, a significantly elevated risk of ALS death among survivors of melanoma [SMR = 1.49 (95 % (CI), 1.17-1.85)] and of tongue cancer [SMR = 2.57 (95 % CI, 1.41-4.32)], and a significantly reduced ALS death risk among prostate cancer survivors [SMR = 0.86 (95 % CI, 0.76-0.96)].

Conclusions: Cancer at certain sites may be related to risk of ALS death. Possible biologic factors linking ALS to these cancers are discussed. Future studies should attempt to confirm these associations using incident ALS outcomes. Establishing relationships between cancer and neurodegenerative diseases, such as ALS, opens new opportunities for understanding related pathophysiologic and therapeutic possibilities for these diseases.