Amyotrophic lateral sclerosis mortality in 1.9 million US cancer survivors.

Background: Large cancer registries offer the opportunity to explore and generate hypotheses about the pathogenesis of cancer and other diseases, including neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS).

Methods: Using data from nine population-based cancer registries of the Surveillance, Epidemiology, and End Results (SEER) Program of the US National Cancer Institute (NCI) and death certificates, we followed 1.9 million cancer survivors who were diagnosed between 1973 and 2000 and who survived at least 1 year, through the year 2000. The outcome of interest was the standardized mortality ratio (SMR) of observed to expected ALS deaths among cancer survivors. To assess the validity of the study design, we also examined associations with Parkinson's disease mortality, which we expected to be inversely associated with smoking-related cancers.

Results: There was no significantly increased risk or deficit of ALS mortality for all cancer sites combined (SMR = 1.0). Parkinson's disease mortality was, as expected, significantly and inversely associated with smoking-related cancers. Both ALS and Parkinson's disease mortality were significantly elevated following melanoma (SMR = 1.6; 95% CI = 1.1-2.2; SMR = 1.5; 1.2-1.8, respectively). Contrary to previous hypotheses, ALS was unrelated to lymphomas or lymphoproliferative malignancies and was not associated with smoking-related cancers.

Conclusions: In this exploratory study, we observed a modest, significant association between melanoma and both ALS and Parkinson's disease mortality. It would be useful to explore these findings in other large national databases that are able to link cancer and ALS and Parkinson's disease.