Sleep apnea can drive the development of aggressive multiple myeloma in mice resistant to the cancer, a study found, suggesting that the sleep disorder is a modifiable risk factor for this disease.
Treating sleep apnea, breathing that starts and stops repeatedly during sleep (also known as chronic intermittent hypoxia), may help to prevent multiple myeloma or improve its treatment, its researchers suggest.
Their study, “Chronic intermittent hypoxia enhances disease progression in myeloma-resistant mice,” was published in the American Journal of Physiology, Integrative and Comparative Physiology.
Obesity is the only known modifiable risk factor for multiple myeloma, but the mechanisms by which obesity might promote myeloma are poorly understood.
Sleep apnea — which is more common in obese people, although linked to many factors — appears to stimulate the growth of solid tumors, such as lung, breast, and colon cancer, and to associate with a poorer prognosis, as these tumors tend to be more aggressive. However, the link between sleep apnea and blood cancers has not been explored.
Researchers at the University of Iowa speculated that sleep apnea could be the link between obesity and multiple myeloma. To prove their hypothesis, they studied the effects of sleep apnea on a mice model that is normally resistant to this blood cancer.
“Multiple myeloma is a serious type of cancer, and it is incurable right now,” Mahmoud Ali, the study’s lead author and a postdoctoral researcher at the University of Iowa, said in a press release. “We are trying to look at what could be a modifiable factor so we can prevent or decrease the risk of people developing cancer.”
Mice were subjected to sleep apnea conditions (10 hours a day of intermittent hypoxia or low oxygen), static hypoxia, or normoxia (normal oxygen levels; a control group) for seven days, and then were injected with a rodent version of malignant multiple myeloma cells. The mice then underwent another 28 days of continuous altered or normal oxygen levels.
Mice exposed to sleep apnea conditions “developed significantly more MM [multiple myeloma] than animals in the control group,” with the cancer found in 67% of these mice compared to 12% of normal oxygen mice. Those given static hypoxia showed no significant differences in the disease.
Multiple myeloma’s more aggressive growth in sleep apnea mice was “evidenced by hindlimb paralysis, gammopathy, bone lesions, and bone tumor formation,” the researchers wrote.
Cancer cells were mostly found within the bone marrow, which is where multiple myeloma normally develops in patients.
“We propose that sleep-disordered breathing could be a unique, targetable risk factor in multiple myeloma. If [sleep apnea] promotes a pro-tumor bone marrow microenvironment generally, it may also affect the development and progression of additional marrow-resident cancers,” the study concluded.
“Treating sleep apnea might be something we could do more to reduce the risk of getting myeloma or to increase the effectiveness of treating the disease,” said Michael Tomasson, a professor at the University of Iowa and a study researcher.
Melissa Bates, the study’s principal investigator and an assistant professor at Iowa, said that treating sleep apnea might also influence the way myeloma patients respond to cancer therapy.
The researchers are now studying if multiple myeloma patients at their university hospital have sleeping disorders, and if treating apnea in those who do might affect their symptoms, response to chemotherapy, and survival rate.