In Taiwan, researchers found patients with Parkinson's disease may be at greater risk of 16 different types of cancer.
According to the research team - including Dr. Pan-Chyr Yang, of the National Taiwan University College of Medicine in Taipei - more than 25 epidemiological studies have investigated the link between Parkinson's disease and cancer over the past 50 years.
While the majority of these studies have found a reduced risk of cancer among patients with Parkinson's disease, some studies have identified an increased risk of certain cancers among patients with the brain disorder, making the studies conflicting.
What is more, Dr. Yang and colleagues note that most of these studies were conducted in Western populations, with very few including East Asian populations.
As such, the team decided to investigate the association between Parkinson's disease and cancer among a Taiwanese population.
They publish their findings in JAMA Oncology.
Parkinson's patients in their 50s at greatest cancer risk
The researchers used the Taiwan National Health Insurance Database to identify 62,023 patients who had been diagnosed with Parkinson's disease between 2004 and 2010, alongside 124,046 individuals without Parkinson's.
All patients were followed until 31st December 2012 or until one of the following occurred: a cancer diagnosis, withdrawal from the Database, loss to follow-up or death.
Compared with participants free of Parkinson's, those with the condition were found to be at greater risk of 16 cancers, including brain, lung, colorectal, kidney, prostate and cervical cancers, as well as lymphoma/leukemia and skin cancers - including melanoma. The highest risk of cancer was found among Parkinson's patients aged 50-59.
However, Parkinson's disease was not associated with increased risk of breast, ovarian or thyroid cancers.
Based on these findings, the authors "conclude that Parkinson's disease is a risk factor for most cancers in Taiwan," noting that further studies are warranted to determine whether their results may apply to other populations in East Asia.
The authors add:
"The striking differences between our study and the previous studies in Western cohorts suggest the importance of ethnicity and environmental exposures in disease pathogenesis."
Though they are unable to explain why Parkinson's appears to be linked to greater risk of cancer in the Taiwanese population, they state that one explanation could be mutations in the PARK2 gene, explaining that mutations in these genes have been linked to both cancer and early-onset Parkinson's.
They point out, however, that further research is warranted to determine the exact mechanisms underlying the relationship between Parkinson's and increased cancer risk.
The team says there are some limitations to their study. For example, incidence of Parkinson's disease was identified through medical records, so it may have been underestimated. The researchers were also unable to identify the smoking status of participants - a factor that may have influenced cancer incidence.
Earlier this week, Medical News Today reported on a study published in JAMA Internal Medicine, in which researchers estimated that almost half of all deaths from 12 cancers are caused by smoking.