Chronic intermittent is a challenge experienced by patients with obstructive sleep apnea (OSA). It was well documented that continuous or very low-frequency intermittent hypoxia increase tumor growth. However, whether the high frequency intermittent hypoxia characterizing OSA (up to 60 event/h) enhances tumor progression and metastasis remained unknown. Very recent data in animal models and in patient populations have provided solid evidence on a positive relationship between OSA and cancer. Mice with injected subcutaneous melanoma cells showed a two-fold tumor growth rate when subjected to intermittent hypoxia mimicking OSA as compared with control animals breathing normoxic air (1). This enhanced tumor progression was associated with increased tumor vasculatisation and correlated with increased circulating levels of vascular endothelial growth factor (2). This mice model of OSA also showed that metastasis from the primary tumor to the lung was increased in the animals subjected to intermittent hypoxia simulating OSA as compared with normoxic controls (3). Enhancement of cancer progression by intermittent hypoxia has been observed in mouse tumors other than melanoma (4). Very recent experimental data strongly suggest that the increase in tumor progression caused by intermittent hypoxia is boosted through immune activation (4). Moreover, data in humans confirm the observed cancer-OSA association revealed by research in animal models. Increased cancer mortality was observed in two different cohorts: in 1546 subjects of the general population followed-up for 22 years (5) and in 5320 patients with suspected OSA followed-up for 4.5 years (6). In both cases, cancer mortality was significantly associated with the severity of nocturnal hypoxemia. A more recent pilot study has shown that human melanoma progression is associated with the severity of OSA (7). In conclusion, the data obtained in animal models and in patient studies strongly suggest that there is an increased cancer risk in patients with OSA. However, further extensive research is required to substantiate the potential clinical impact of the association between OSA (via intermittent hypoxia) and cancer.