Immunohistochemistry in the diagnostic evaluation of breast lesions.

Most diagnoses in breast pathology can be rendered after careful evaluation of a high quality hematoxylin and eosin-stained tissue section. However, a significant number of both benign and malignant lesions can show variable morphologic patterns and significant histologic overlap, leading to diagnostic uncertainty. These challenges and complexities have opened the door to an expanding role for immunohistochemistry (IHC) as an important diagnostic adjunct for solving frequently encountered problems in breast pathology. Although IHC has proven to be a powerful tool in helping to resolve difficult cases, the results of such studies should always be carefully interpreted within the morphologic context for each lesion. This article will briefly review some of the more common circumstances in which IHC has been shown to be useful in diagnostic breast pathology.