To treat or no to treat: HER2 equivocal is the matter!

With the introduction of the 2013 American Society of Clinical Oncology (ASCO)/College\r\nof American Pathologists (CAP) guidelines for human epidermal growth factor receptor type 2 (HER2)\r\ntesting, some authors noticed an increase in equivocal HER2 determinations. Indeed, many retrospective\r\nassessments showed an increase of up to 14% in the number of equivocal cases by immunohistochemistry\r\nand fluorescence in situ hybridization. In these cases, if after reflex testing with the same and/or an\r\nalternative specimen the HER2 test result is deemed to be equivocal, the ASCO/CAP guidelines recommend\r\nto consider HER2-targeted therapy. However, due to the absence of prospective data on the efficacy of\r\nanti-HER2 therapy in equivocal HER2 breast cancer (BC), the therapeutic decision is extremely complex,\r\nespecially in the adjuvant and neoadjuvant settings. In this perspective paper, we analyse the available\r\nretrospective data aiming to answer to the dilemma whether to treat or not to treat HER2 equivocal cases\r\nwith a HER2-targeted therapy