RESUMO
In breast pathology, immunohistochemistry (IHC) allows the resolution of differential diagnostic problems regarding a primary tumor. With a basic antibody panel, it allows precise identification of undifferentiated, morphologically similar or unusual tumors. In case of doubt on invasiveness, IHC reveals the epithelial basement membrane and myoepithelial cells. A specific marker of breast tissue does not exist at the present time, but IHC guides the physician in the direction of breast in case of unknown secondary tumor or to confirm the primary breast site or to indicate the breast as primary site in case of two morphologically similar tumors. For the prognosis, IHC improves the detection of occult metastases (serous fluids, node, bone marrow, etc.). During the last few years, its indications have increased considerably with the possibility of performing, with paraffin slides, the detection of estrogen and progesterone receptors, growth factors and their receptors, oncoproteins, cell proliferation-related proteins, etc. The effects on the prognosis and chemotherapy sensitivity evaluation are obvious. But the pathologists must be very demanding because the clinical use of these new data by the physicians will be possible only after an excellent methodological and clinical validation in relation to the classical prognostic factors.