ABSTRACT
Over the last few years, it has become apparent that B1BCs have a rather specific
phenotype, i.e., these infiltrating breast cancers show expression of proteins that are
usually only found in basally situated cells in the normal breast. This phenotype is
negatively associated with expression of both estrogen receptor and the oncogene erbB-2, also known as HER2. The tumors are often of high histological grade and show a high degree of aneuploidy. By contrast, it has been much harder to identify a specific
phenotype for B2BCs, although these cancers can usually be distinguished from B1BCs.
The clinical implications of the pathological features of B1BCs and B2BCs are beginning
to be used clinically by cancer geneticists, and to a lesser extent, by oncologists.
