A new study links the intermittent interruption of breathing that occurs in patients with obstructive sleep apnea (OSA) to enhanced proliferation of melanoma cancer cells and increased tumor growth in mice, according to researchers in Spain. The study also found tumor cells of OSA mouse models tended to contain more dead cells, indicating a more aggressive type of cancer.
The results of the study were presented at the ATS 2011 International Conference in Denver.
"To our knowledge, this study is the first one providing experimental evidence that a high-rate intermittent lack of oxygen, or hypoxia, mimicking the one experienced by OSA patients enhances tumor growth," said Ramon Farre, PhD, professor of physiology at the University of Barcelona School of Medicine Biophysics and Bioengineering Lab.
In this study, mice injected with melanoma tumor cells were divided between two groups. In the first group, mice were exposed to intermittent hypoxia, where oxygen was restricted for 20-second periods at a rate of 60 periods per hour for 6 hours per day, and normal oxygen levels for the remainder of the day. In the second group, mice received normal levels of oxygen (normoxia). Tumor volume was measured throughout the study and at the end of the study period. At the end of the 14-day study period, tumors from all mice were removed and weighed and tumor necrosis (indicated by the numbers of dead cells present) was measured to determine the aggressiveness of the tumors.
The authors found that while tumor volume progressively increased with time in both the intermittent hypoxia and control groups, the increase was higher in the mice subjected to intermittent hypoxia. Tumor weight and necrosis in the intermittent hypoxia group were almost two times those of the tumors in the control group.
Future studies would need to evaluate whether intermittent hypoxia also triggers the initial formation of tumors and whether it promotes metastasis, or spread of tumors from one organ to another. Because this study focused on melanoma, Farre said additional studies should also explore whether intermittent hypoxia affects other types of cancer.
Extended population studies should also determine if there is a relationship between the incidence of cancer and the severity of OSA, as well as addressing the issue of obesity, which has been linked with OSA.