Comorbid cancer in Parkinson's disease

The aim of this article was to evaluate cancer occurrence before and after diagnosis of Parkinson's disease (PD). We investigated 692 patients newly diagnosed with PD and 761 age- and sex-matched control subjects identified during two periods (1994-1995 and 2000-2003) within Kaiser Permanente Medical Care Program of Northern California. Primary cancers were searched and dated, and all participants were followed up until the end of membership, death, or December 31, 2008. We used unconditional logistic regression to evaluate the PD-cancer association before the date of PD diagnosis or the index date and Cox proportional hazards regression to evaluate the PD-cancer association after the index date. Nearly 20% (140 of 692) of the PD patients and 25% (188 of 761) of the non-PD controls had ever had a cancer diagnosis. Before the index date, the prevalence of cancer was not significantly lower in patients with PD (8.1% PD vs. 9.2% controls; OR = 0.83; 95% CI 0.54-1.3). After the index date, the risk of developing a cancer did not differ between PD cases and controls (relative risk [RR] = 0.94; 95% CI 0.70-1.3). Among specific cancers, melanoma was more common among PD cases (before PD, OR = 1.5; 95% CI 0.40-5.2; after PD, RR = 1.6; 95% CI 0.71-3.6), but independent of dopaminergic therapy. Cancer occurrence is not significantly lower among patients with PD. The positive association between PD and subsequent melanoma merits further investigation, as it does not seem to be attributable to dopaminergic therapy, pigmentation, or confounding by smoking.