There are three possible scenarios that could account for the variation in the location of the tumors within the simplex map: (1) The cancer cells within any specific tumor are relatively pure representatives of Luminal, Basal and HER2 subtypes and that the map position reflects their proportions within the tumor; (2) The cancer cells within a tumor are mostly homogeneous and the position reflects their similarity to the three subtypes; (3) A hybrid between the first two scenarios. This evidence concerns the gene ERBB2 and cancer.