In breast cancer, the algorithm distinguished 3 biologically meaningful subgroups: group 13 captured a pure basal-like subtype (all 13 basal tumors); group 5 combined all HER2 (9 of 10) and LumB (16 of 16) cases with most LumA (18 of 29) samples, reflecting a nonbasal, high-risk profile; and group 1 comprised predominantly LumA tumors (9 of 11) alongside normal controls, defining a lower-risk, luminal A–driven cluster. Here, ERBB2 is linked to breast cancer.