Diagnostic immunohistochemistry: what patients should know

The test is performed in a laboratory on a sample obtained during a biopsy or operation. Antibodies bind to selected proteins in the cells, producing a visible pattern that is assessed alongside the tissue's appearance under a microscope.

A pathology report may describe a marker as positive, negative, focal or present with a particular intensity or location. These terms refer to staining in the submitted tissue; they are not a diagnosis by themselves. The pathologist combines the pattern with cell shape, tissue structure, clinical details and other test findings.

A panel of markers is often more informative than a single stain because different cell types can share proteins. The findings may help establish where abnormal cells originated, distinguish between conditions that look similar or identify a feature relevant to treatment selection. An unclear pattern can lead to additional stains, molecular testing or review of more tissue.

Arrange a discussion with the clinician who requested the test and bring the full pathology report. Ask which markers were tested, how the combined pattern supports the stated diagnosis and whether any result affects treatment planning.

If the report says the sample was limited, indeterminate or needs correlation, confirm what will resolve the uncertainty. The next action might be review of existing slides, another laboratory method, imaging, a multidisciplinary discussion or collection of an additional sample. Do not interpret an isolated positive marker as proof of a particular cancer.

Immunohistochemistry itself is carried out on tissue outside the body, so concerns after sampling usually relate to the biopsy or operation. Contact the treating team promptly for increasing redness, warmth, swelling, discharge, fever, worsening pain or bleeding that does not settle with the instructions you were given. Seek urgent care for severe bleeding, fainting, marked breathing difficulty or rapidly worsening symptoms.

If you have received a report but no follow-up arrangement, contact the requesting clinic so the complete result can be explained in context and the next step is not delayed.

Useful questions include: What diagnosis does the full staining pattern support? Were the controls and tissue sample adequate? Does the report identify the likely origin of the cells? Are further stains or molecular tests needed? Will these findings change my treatment choices or the timing of my next appointment?