A researcher at the Hospital Clínic de Barcelona in Spain presented on Friday his research that revealed a possible connection between sleep apnea and cancer development at the European Association of Urology Annual Congress in Munich, Germany.
Sleep apnea is a disorder that involves involuntary pauses in breathing while the patient is asleep. This is why patients are given a sleep apnea oral appliance therapy to help them with this kind of sleeping disorder.
The disorder affects more than 18 million Americans, according to the National Sleep Foundation. According to the Mayo Clinic, sleep apnea is characterized by loud snoring, breathing cessation, sudden awakenings and shortness of breath. It is especially prevalent in patients who carry excessive weight and have narrow airways. According to the study, presented by Antoni Vilaseca Cabo, these pauses in breathing help to increase blood vessel growth in tumors and promote the development of cancer.
“This study looked at the effect on vessels formation of intermittent hypoxia on a mouse model of kidney cancer,” Vileseca wrote in an email. “Previous studies suggested that [intermittent hypoxia] is associated with worse mortality and aggressiveness in some types of cancer. However, the mechanisms are not completely known.”
Gerald Denis, pharmacology and medicine professor at the Boston University School of Medicine, said the study was “intriguing,” as it linked together “two different, well-known literatures.”
“There’s a lot of research done on angiogenesis and tumor metastasis potential, and there’s quite a lot done in sleep apnea, but they’ve never really been brought together in this new way before,” he said. “These are two different groups of patients and different groups of clinicians that don’t normally talk to each other.”
According to a Friday press release, the study investigated 24 mice with kidney tumors and exposed 12 of them to fluctuating oxygen levels in order to simulate intermittent hypoxia. As result, the research group found an increase in the vascular endothelial growth factor, which stimulates the formation of blood vessels.
“This [is] intriguing, that this lack of oxygen is being detected in the tissues, and it’s creating angiogenesis throughout the body and throughout these other growth factors that create new blood vessel formation,” Denis said. “We know independently this is bad for cancer progression, because as soon as cancers become more vascularized, these tumors are fed better … [and] have more options to metastasize through the blood system.”
These findings hold promise for determining the intensity of cancer development.
“This is a preliminary study in mice,” Vileseca said. “If confirmed in humans, sleep apnea could be a prognostic factor of aggressiveness.”
While this discovery reveals a new, possible link for cancer development, further studies must be done in order to make it applicable to humans. Denis said he believes that the next step is to look for the exceptions.
“You want to see who has sleep apnea, and possibly a cancer diagnosis, but they don’t progress,” he said. “There are going to be people for which this doesn’t apply, so you want to know what characterizes them or why are they protected. Conversely, there are going to be people who don’t have sleep apnea, who have metastatic cancer. So why are they at risk?”
Other experts, such as Adam Lerner, a professor of medicine at BUSM, agree that more work needs to be done in order to strengthen the evidence of this correlation. Lerner suggested an idea for how he would collect data to make a more convincing argument.
“If one had an animal model where tumors developed spontaneously at higher incidents than normal and then subject those mice to intermittent hypoxia and look to see whether there is a change in the overall incidence of kidney tumor development, that would be a much more difficult experiment to do,” he said. “It would take a much larger number of mice and would be difficult because you would have to expose them to this intermittent hypoxia for a longer time.”
