The mouse study suggests sleep apnea may worsen outcomes for cancer patients through hypoxia-induced blood vessel growth in tumors.
Lead researcher Dr. Antoni Vilaseca, of the Hospital Clinic De Barcelona in Spain, and colleagues recently presented their findings at the European Association of Urology (EAU) Congress in Munich, Germany.
Sleep apnea is a disorder in which a person has shallow breaths or one or more pauses in breathing during sleep. Such pauses can last from seconds up to a few minutes, and they can happen as many as 30 times in an hour.
Obstructive sleep apnea is the most common form of the condition, where the airway becomes blocked or collapses during sleep.
Sleep apnea affects more than 18 million Americans in the US. Risk factors for the disorder include a small upper airway, smoking, alcohol use, being overweight and having a large neck, small jaw or a large overbite.
Previous research has associated sleep apnea with worse outcomes for cancer patients. A 2012 study reported by Medical News Today, for example, suggests that sleep apnea increases the risk of cancer death.
While the exact mechanisms underlying the possible link between sleep apnea and cancer have been unclear, researchers have suggested that the intermittent hypoxia that comes with the sleep disorder - a reduction in the amount of oxygen that reaches body tissues - may play a role.
Intermittent hypoxia increased cells key to blood vessel growth in tumors
To further investigate, Dr. Vilaseca and colleagues studied 24 mice with kidney tumors, 12 of which were exposed to varying oxygen levels, simulating the intermittent hypoxia caused by sleep apnea.
The researchers found that the tumors in mice that experienced intermittent hypoxia showed an increase in vascular progenitor cells and endothelial cells, compared with the tumors of mice that were not subject to intermittent hypoxia.
The team explains that these cells can mature to create blood vessels in tumors; blood vessels supply tumors with the resources they need to grow and spread, or metastasize, to other parts of the body.
In addition, the researchers found that mice exposed to intermittent hypoxia also showed an increase in circulating levels of vascular endothelial growth factor (VEGF) - a protein that is known to boost blood vessel formation.
Overall, the team believes the findings indicate that sleep apnea may worsen outcomes for cancer patients through hypoxia-induced blood vessel growth in tumors.
Commenting on the results, Dr. Vilaseca says:
"Patients suffering from obstructive sleep apnea usually suffer from intermittent hypoxia at night. This work shows that intermittent hypoxia has the potential to promote the formation of blood vessels within tumors, meaning that the tumors have access to more nutrients.
This is of course an early animal study, so we need to be cautious in applying this to humans. Nevertheless, this work indicates a plausible mechanism for just why conditions which restrict oxygen flow to tissues, like sleep apnea, may promote cancers."
Prof. Arnulf Stenzi, chair of the EAU Congress Committee - who was not involved in the study - hails the findings as "remarkable" because they show how oxygen deficiency can influence renal tumor growth.
"It may be postulated that increased oxygenation of the blood may be the underlying mechanism why not smoking or giving up smoking, regular sport activity (especially endurance type sports), reducing the body mass index (BMI) and other lifestyle changes that increase tissue oxygenation have a supportive beneficial effect on better outcomes in renal cell cancer as well as other tumor types," he adds.
Last year, MNT reported on a study linking heavy snoring and sleep apnea to earlier cognitive decline.