Effects of Parkinson’s disease on survival in cancer survivors: a retrospective, multicentre cohort study in Japan

Aging populations and advances in medical care have contributed to an increase in the number of patients with Parkinson's disease and cancer survivors. However, the effects of Parkinson's disease on the survival of patients with cancer remain unclear. We aimed to investigate the effect of Parkinson's disease on the prognosis of patients with cancer. This retrospective multicentre cohort study used data from the Osaka Cancer Registry, which was linked to administrative data obtained between 2010 and 2015 in Japan. Patients with cancer who were followed up for 5 years after cancer diagnosis were categorized into Parkinson's disease and non- Parkinson's disease groups according to the presence of comorbid Parkinson's disease. We compared survival between the two groups using Kaplan-Meier analyses. Cox proportional-hazard models were used to assess the hazard ratio and 95% confidence interval of Parkinson's disease for all-cause mortality. Propensity-score matching was used to validate the analysis and address differences in clinical characteristics between the groups. The cohort included 118 999 patients with cancer and 1049 patients (0.9%) with comorbid Parkinson's disease. The patients in the Parkinson's disease group were older and had lower mobility than those in the non- Parkinson's disease group. Kaplan-Meier analysis revealed that the 5-year survival rate after cancer diagnosis was significantly worse in the Parkinson's disease group than in the non- Parkinson's disease group (54% versus 70%, <i>P</i> < 0.001). Comorbid Parkinson's disease was independently associated with 5-year mortality [crude hazard ratio (95% confidence interval), 1.72 (1.56-1.88), <i>P</i> < 0.001]. This association remained significant after adjusting for potential confounders [adjusted hazard ratio (95% confidence interval), 1.37 (1.25-1.51), <i>P</i> < 0.001]. When the survival analysis was stratified by mobility, no intergroup difference in prognosis was observed among patients with impaired mobility. However, among patients with independent mobility, patients in the Parkinson's disease group had a worse prognosis than those in the non- Parkinson's disease group [crude hazard ratio (95% confidence interval), 1.74 (1.42-2.13), <i>P</i> < 0.001]. Similar results were observed after propensity-score matching. Patients with cancer and comorbid Parkinson's disease had a worse prognosis than those without comorbid Parkinson's disease. The effect varied depending on mobility. These findings highlight the importance of carefully managing Parkinson's disease symptoms and maintaining mobility in cancer patients with Parkinson's disease, as this could potentially improve their prognosis and survival outcomes.