Hx is the protein with the highest binding affinity for heme and, as summarized in the paragraphs above, high levels of Hx have been observed in cancer patients’ body fluids, so that it has been proposed as a biomarker for different kinds of cancer, particularly those highly invasive and metastatic (see Table 1 for a comprehensive summary of the observations emerged from the works reported in the present manuscript). This evidence concerns the gene HPX and cancer.