Patients with obstructive sleep apnea (OSA) have an increased risk of cancer but it has not been clear whether this is due to the OSA itself or to related risk factors for cancer, such as obesity, cardiometabolic disease, and lifestyle factors, says Andreas Palm, a researcher and senior consultant at Uppsala University, Sweden.

Palm recently presented a large study on obstructive sleep apnea and cancer risk at the European Respiratory Society (ERS) International Congress in Barcelona, Spain. “Our findings show that oxygen deprivation due to OSA is independently associated with cancer,” he says in a release.

In “Cancer prevalence is increased in obstructive sleep apnea – the population-based DISCOVERY study,” Palm and colleagues looked at data from 62,811 patients five years prior to the start of treatment for obstructive sleep apnea in Sweden. Between July 2010 and March 2018, patients were treated with CPAP. The researchers linked these data with data from the Swedish National Cancer Registry and socio-economic data from Statistics Sweden.

The researchers took account of factors that could affect the results such as body size, other health problems, and socio-economic status. They matched 2,093 patients with obstructive sleep apnea and a diagnosis of cancer up to five years before OSA diagnosis with a control group of 2,093 patients with OSA but no cancer.

“We found that patients with cancer had slightly more severe OSA, as measured by an apnea hypopnea index average of 32 versus 30, and an oxygen desaturation index [ODI] of 28 versus 26,” he says. “In further analysis of subgroups, ODI was higher in patients with lung cancer (38 versus 27) prostate cancer (28 versus 24) and malignant melanoma (32 versus 25).

“The findings in this study highlight the need to consider untreated sleep apnea as a risk factor for cancer and for doctors to be aware of the possibility of cancer when treating patients with OSA. However, extending screening for cancer to all OSA patients is not justified or recommended by our study results.”

The study only looked at data from one point in time and it cannot show that obstructive sleep apnea causes cancer, only that it is associated with it. Some important lifestyle factors such as physical activity and food preferences were not captured on an individual basis in the study. The main strength of the study is its large size and the high quality of data on cancer diagnosis and OSA.

In the future, Palm and his colleagues plan to increase the number of patients and to follow the patients over time to study the potential influences of CPAP treatment on cancer incidence and survival. “The association between OSA and cancer is less well established than the link with diseases of the heart and blood vessels, insulin resistance, diabetes, and fatty liver disease,” he says. “Therefore, more research is needed, and we hope our study will encourage other researchers to research this important topic.”

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