MedPage Today's new "Beyond Diagnosis" series opens with Cleveland Clinic breast oncologist Megan Kruse explaining how pathologists' reports guide early HER2-positive breast cancer treatment. Kruse describes the pathology report as the "roadmap to care," with immunohistochemistry (IHC) results scored from 0 to 3. Scores of 0 or 1+ are considered negative, while 3+ is definitively positive and calls for chemotherapy plus HER2-targeted therapy. A 2+ result is equivocal and prompts fluorescence in situ hybridization (FISH) as a secondary test.
Equivocal results can persist even after FISH. In those cases, Kruse says clinicians may repeat testing on another biopsy site, have another pathologist review the sample, or obtain a new biopsy. Such cases go to tumor board, where multidisciplinary teams decide next steps. She notes that when any HER2 positivity is possible, the tendency is to give HER2-targeted agents the benefit of the doubt, because the drugs are highly effective and untreated disease can be aggressive.
Newer categories like HER2-low and HER2-ultralow have complicated the picture, especially for informed patients. Kruse stresses that these labels are relevant mainly for metastatic breast cancer, not for stage I-III disease, where the traditional positive/negative distinction still drives upfront treatment. Hormone receptor status also matters — about half of HER2-positive tumors express hormone receptors — though the interview's discussion of that topic is cut off in the transcript.