Dr Rimm on Limitations With IHC Testing in HER2-Low and HER2-Ultralow Breast Cancer

David Rimm, MD, PhD, Anthony N. Brady Professor of Pathology, professor, medicine, Medical Oncology, Yale School of Medicine; director, Physician Scientist Training Program, Pathology Research, director, Tissue Microarray Facility, director, Yale Pathology Tissue Services, Pathology, Yale Cancer Center, discusses the limitations of current immunohistochemistry (IHC) diagnostic kits for patients with HER2-low and HER2-ultralow breast cancer.

Researchers need to design diagnostic tests in a manner that optimizes pathologists’ ability to achieve reproducible results, Rimm begins, adding that the current tests do not meet this standard. In his view, the breast cancer field should move beyond relying on pathologists to subjectively “read” tests, and instead focus on precise measurements. Measurements, rather than subjective readings, are objective, standardized methodsof quantifying a target, such as providing the concentration of a biomarker on a slide in a defined unit, he states. This is an aspirational goal, and only a few laboratories globally are currently capable of such measurements, according to Rimm. However, Rimm believes that transitioning toward this model is essential for providing the best care to patients.

In fields like lung cancer, for instance, tests are used to measure EGFR expression levels to determine patient eligibility for TKIs, he continues. This testing approach relies on objective measurements rather than subjective readings by pathologists, he explains. Measurements allow for reproducibility and enable quality control, ensuring that the machines used are properly calibrated and functioning consistently, Rimm emphasizes.

Rimm believes that the future of IHC lies in such standardized measurements rather than subjective readings, but that achieving this change will require significant time. In the meantime, the oncology field must work to standardize current IHC reading methods by ensuring uniformity in the machines used, addressing one of the weakest points in the current system, he notes. Ultimately, future tests should be designed to be both reproducible and manageable for pathologists, Rimm concludes.