Sleep-disordered breathing (SDB) is associated with an increased risk of cardiovascular, metabolic and neurocognitive disorders. New studies show that it also implies a greater risk of developing tumors, and even dying from cancer. Experimental animal studies led by researchers from the August Pi i Sunyer Biomedical Research Institute (IDIBAPS), the University of Barcelona and the Hospital Clínic of Barcelona have shown that repeated episodes of hypoxia (an inadequate supply of oxygen that characterizes sleep apnea) are linked to accelerated cancer progression. New experimental results are the first to suggest that sleep apnea may be associated with increased cancer mortality in humans.
Animal experiments that gave rise to this hypothesis were led by professor at the UB Ramon Farré and his team of Respiratory Biophysics and Bioengineering from the Department of Physiological Sciences I of the Faculty of Medicine of the UB and of the IDIBAPS. Now, a collaboration with the team of Dr. F. Javier Nieto, from the Department of Population Health Sciences of the School of Medicine and Public Health at the University of Wisconsin (USA), has demonstrated in a large cohort of patients that sleep apena increases the risk of cancer mortality. Dr. Ramon Farré collaborates on a regular basis with Dr. Josep Maria Montserrat, from the Pulmonology Service at the Hospital Clínic of Barcelona, member of the IDIBAPS and lecturer at the Department of Medicine of the UB. Experimental studies in a cohort of Spanish patients suffering from apnea, funded by the Spanish Society of Pulmonology and Thoracic Surgery (SEPAR), have demonstrated that the risk of cancer may increase in patients with sleep apnea. This research has been supported by CIBERES, a multidisciplinary research network in respiratory diseases.
In vitro and animal studies show that intermittent hypoxia promotes angiogenesis and tumor growth. Therefore, researchers have examined 22-year mortality data on 1,522 subjects from the Wisconsin sleep cohort. This prospective study has analyzed predictors and natural history of sleep disorders using techniques of polysomnography. The results of the study, whose main authors are doctors Javier Nieto and Ramon Farré, were presented on Sunday 20 May during the International Conference of the American Thoracic Society (ATS 2012) in San Francisco. They have also been published in the journal The American Journal of Respiratory and Critical Care Medicine (AJRCCM).
In this large cohort, the risk of all-cause mortality and of cancer mortality was adjusted for age, sex, body mass index, smoking, and other factors. Compared to subjects without sleep apnea, the relative hazards of cancer mortality were 1.1 for mild SDB; 2.0 for moderate SDB, and 4.8 for severe SDB. This means that, in case of developing cancer, the fact of having severe sleep apnea may accelerate cancer progression. However, further studies should be carried out to demonstrate whether patients suffering from aggressive cancer could benefit from early diagnosis and treatment of sleep-disordered breathing.
On the other hand, the cohort analyzed as part of SEPAR’s sleep study group gathers data on 5,246 patients who were diagnosed with sleep apnea in seven Spanish hospitals between 2000 and 2007. This study, carried out by Dr. Francisco Campos from the Valme Hospital (Sevilla) and co-ordinated by Dr. Josep Maria Montserrat, has shown that 5.7 % of patients with sleep-disordered breathing were diagnosed with cancer during the follow-up period, and that patients with the most severe apnea proportionally increased the risk of suffering from one. In an independent study also presented at the ATS 2012 conference, the group from the IDIBAPS-UB-Clínic put forward new data obtained from mice. This work shows that the effect of intermittent hypoxia on cancer growth is considerably stronger in lean mice than in obese mice.
Therefore, it is necessary to confirm with further studies the relationship between sleep-disordered breathing and cancer mortality. If these hypotheses are validated, further studies will have to analyse whether the diagnosis and treatment of SDB in patients with aggressive cancer might be indicated to prolong survival. Researchers from the IDIBAPS-UB-Clínic will continue working, together with renown collaborators such as those from the University of Wisconsin and the Spanish experts from SEPAR and CIBERES, to deepen knowledge about the relationship between sleep-disordered breathing, obesity and cancer mortality.