According to the role of iron metabolism in shaping a protumor TME, we recently described a specific subset of TAMs expressing a high level of heme oxygenase 1 enzyme (HO-1) and reported that the expansion of blood HO-1+ monocytes is associated with both increased frequency of HO-1+ TAMs and poor prognosis, in both preclinical fibrosarcoma and melanoma models, as well as in stage III-IV melanoma patients [23]. This evidence concerns the gene HMOX1 and fibrosarcoma.