Recent studies have indicated that patients with sleep apnea may be associated with worse cancer outcomes. Now a new animal study, presented at the European Association of Urology Congress in Munich, uncovers a possible mechanism that may underlie this link.
A group of Spanish-US researchers have used a mouse model to show that intermittent hypoxia (where a tissue or organ does not get enough oxygen) promotes the formation of blood vessels within tumors, probably due to an increased production of vascular endothelial growth factor (VEGF). VEGF is known to promote blood vessels formation.
A team led by Antoni Vilaseca, MD, MS, (Hospital Clínic De Barcelona, Spain) took 12 experimental and 12 control mice with kidney tumors and subjected them to varying oxygen levels to mimic intermittent hypoxia. They found that the mice which had been subjected to intermittent hypoxia showed increases in vascular progenitor cells (6,1 ± 0,76 vs 4,5±1,1; p=0,001) and endothelial cells (4±0,8 vs 2,5±1; p=0,013) within the tumors; these cells may later mature to form blood vessels in the tumors. Circulating VEGF was also increased in the mice which had undergone hypoxia (306±93 vs 204±45 pg/mL; p=0,001), although other factors such as tumour growth, were not affected.
Lead researcher Vilaseca says in a release: “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 tumours have access to more nutrients.”
He adds, “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.”
Professor Arnulf Stenzl (Tübingen), chair of the EAU Congress Committee, says: “Although this is an experimental study, it is remarkable, because it demonstrates the influence of oxygen deficiency on the growth of renal cell carcinoma tissue (both primary tumor as well as metastases). 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, 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.”