Using spheroids from human breast cancer cells, Werno and colleagues presented additional experimental evidence for a role of HIF-1α for M1 polarization [100]. In vivo confirmation of these results is missing thus far, but as more and more reliable antibodies against M1/M2-specific markers are available and FACS-based characterization of the tumor immune infiltrate prevails this should only be a matter of time. Here, HIF1A is linked to breast cancer.