Sleep apnea may drive tumour growth by promoting blood vessel formation

A NEW study sheds light on how sleep apnea might worsen outcomes for cancer patients, revealing that hypoxia – a consequence of the sleep disorder – may promote blood vessel growth in tumours. 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. To further investigate, Dr. Vilaseca and colleagues studied 24 mice with kidney tumours, 12 of which were exposed to varying oxygen levels, simulating the intermittent hypoxia caused by sleep apnea.
The researchers found that the tumours in mice that experienced intermittent hypoxia showed an increase in vascular progenitor cells and endothelial cells, compared with the tumours of mice that were not subject to intermittent hypoxia. The team explains that these cells can mature to create blood vessels in tumours; blood vessels supply tumours with the resources they need to grow and spread, or metastasise, 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 tumours.
“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 tumours, meaning that the tumours have access to more nutrients. This is of course an early animal study, so we need to be cautious in applying this to humans.

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