HER2 in solid tumors

Identification of HER2 status has become a crucial step in several solid tumors. The well-established three-tier classification of HER2 status (negative-positive-equivocal) has been extended, and nowadays, the terms “HER2-low” and “HER2-ultralow” have been introduced into everyday oncology practice.

The introduction of these new categories highlights the utmost importance of technical issues, particularly the preanalytical handling of tumor samples and the optimal quality of immunohistochemical reactions.

In this review, based on the most recent literature data, the various methods for identifying HER2 status in different solid tumors are described, where available, along with corresponding guidelines. Special emphasis is placed on the potential of antibody-drug conjugates as a novel targeted treatment option for HER2-low tumors.