Myoglobin tames tumor growth and spread.

Tumor growth is accompanied by tissue hypoxia, but does this reduced oxygen availability promote further tumor expansion, resulting in a vicious cycle? In this issue of the JCI, Galluzzo et al. report that increasing oxygen tension in tumor cells by ectopically expressing the oxygen-binding hemoprotein myoglobin indeed affects tumorigenesis (see the related article beginning on page 865). Tumors derived from cells transfected with myoglobin grew more slowly, were less hypoxic, and were less metastatic. These results will spur further mechanistic inquiry into the role of hypoxia in tumor expansion.