Objective: We systematically reviewed studies to investigate a possible association between validated PD diagnoses and cancer risk.

Background: An inverse association between Parkinson’s disease (PD) and overall cancer risk has often been reported. However, a recent meta-analysis reported marked data heterogeneity and bias from different PD definitions has previously been suggested.

Method: PubMed and Google Scholar databases were searched, together with reference lists of retrieved articles ( published 1.1.1980-1.3.2021). Two reviewers independently screened abstracts to identify relevant articles, followed by full-text review of selected articles. The included studies were categorized into category 1 (PD cases were validated by chart review or clinical validation of the search algorithm) and category 2 (registry data with no validation of PD diagnoses). Studies investigating only death certificate data were excluded. Relative risk was presented as the cancer risk of PD patients versus controls. Gender specific results were presented accordingly

Results: We included 25 original articles in the analysis [table1] . In all 17 category 1 studies, ten (59%) found no association between PD and cancer risk, five (29%) found a decreased cancer risk in PD patients (of which one only in women) and two reported an increased cancer risk after PD diagnosis. Of the 11 category 2 studies, six (55%) reported a decreased risk of cancer in PD patients, four (36%) found no difference between cases and controls and one observed an increased risk of cancer risk after the diagnosis of PD. Of the studies that investigated cancer risk before PD diagnosis 38% reported an inverse association between the diseases (one in women only) whereas 44% of those investigating cancer risk after PD diagnosis found no association, 39% found a decreased cancer risk in PD patients (71% of these studies were category 2) and 17% found an increased risk of cancer in patients with PD. Studies reporting increased cancer risk in PD patients had most often small sample sizes.

Conclusion: The majority of studies without PD validation (category 2) showed a decreased risk of cancer, whereas the majority of studies with validated PD diagnoses (category 1) indicated no   difference   in the risk of cancer.  We suggest that the validity of PD diagnoses should be considered in further epidemiological studies to confirm or refute the suggested association with cancer.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/risk-of-cancer-in-parkinsonss-disease-a-systematic-review-of-diagnostic-validity/