['Very recent studies revealed that obstructive sleep apnoea (OSA) is a contributor of the increased incidence and mortality of cancer in humans, but mechanisms of how OSA promotes tumorigenesis remains largely unknown. We investigated whether intermittent hypoxia with and without hypercapnia plays a role in tumorigenesis.', 'First, Sprague-Dawley (SD) male rats (12 weeks old) were subjected to different hypoxia exposures: intermittent hypoxia and intermittent hypoxia with hypercapnia; continuous hypoxia and normal air. The systemic application of chronic fast rate hypoxia with or without hypercapnia mimicked severe OSA patients with apnoea/hypopnea index equivalent to 60 events per hour. Then routine blood tests were performed and the levels of brain derived neurotrophic factor (BDNF) and miR-34a were examined.', 'In contrast to intermittent hypoxia with hypercapnia, both intermittent hypoxia and continuous hypoxia treatments caused significantly higher levels of haematology parameters than normoxia treatments. Compared to normoxia, intermittent hypoxia with hypercapnia exposure resulted in substantial decrease of serum BDNF and, miR-34a in the lower brainstem, while less pronounced results were found in intermittent hypoxia and continuous hypoxia exposure.'] Is intermittent hypoxia with or without hypercapnia associated with tumorigenesis by decreasing the expression of brain derived neurotrophic factor and miR-34a in rats?