What should you know about HER2 by immunohistochemistry?

A pathologist applies an antibody stain to tissue obtained during a biopsy or operation. The pattern and strength of staining are assessed under a microscope and recorded in the pathology report. A result may be described as negative, equivocal, or positive using the laboratory's scoring system. An equivocal result can lead to a different confirmatory test, because treatment decisions should rest on a clear interpretation.

Ask which tissue sample was tested, whether the sample was adequate, and what the exact score means for your cancer. Keep the full pathology report with your imaging and treatment records. If the result does not fit the rest of the findings, ask whether review by another pathology team or additional testing is appropriate. The result is one part of diagnosis and does not by itself describe stage or spread.

The stain itself does not usually create an urgent problem. Seek prompt medical advice for heavy bleeding, increasing redness, pus, fever, or worsening pain after a biopsy. Contact your cancer team quickly if new severe symptoms arise while you are waiting for results, including breathing difficulty, confusion, or sudden weakness.

What is the exact HER2 score and category? Was the sample taken from the main tumour or another area? Is confirmatory testing needed? How could this result change the treatment options being discussed?