However, about half of the HER2 overexpressing tumors are ER-positive and fall into the LB subtype, the normal breast-like group seems to be an artifact, and ER-negative tumors encompass at least three other molecular subgroups: the molecular apocrine (MA) breast tumor group, the interferon-rich subgroup and the claudin-low subtype. The gene discussed is ERBB2; the disease is breast neoplasm.