Immunohistochemistry — Staining Test for Cancer Cells

Immunohistochemistry is a specialised diagnostic process that combines principles of immunology and histology. During testing, pathologists apply laboratory-engineered antibodies to thin slices of biopsied tumour tissue mounted on glass slides. These antibodies are designed to bind exclusively to specific target antigens or proteins expressed by the cancer cells. A chemical marker or fluorescent dye attached to the antibody produces a visible colour change under a standard microscope wherever binding occurs.

Because different cell types and tumours express distinct sets of proteins, this selective staining provides a molecular fingerprint of the tissue. Beyond simply confirming whether cancer is present, immunohistochemistry allows pathologists to distinguish between malignancies with similar microscopic appearances, identify the primary site of metastatic tumours, and measure the abundance of predictive biomarkers.

An accurate diagnosis is the cornerstone of effective cancer management. Immunohistochemistry provides crucial details that directly influence clinical staging, prognostic assessment, and therapeutic selection. For many malignancies, standard chemotherapy has been replaced or supplemented by medicines designed to block specific molecular pathways. IHC testing tells your oncologist whether your tumour possesses the biological targets required for these therapies to work. Knowing these results prevents exposure to treatments unlikely to help, guides clinical trial eligibility, and ensures your treatment plan is tailored precisely to your tumour's specific characteristics.

IHC is performed on formal tissue samples collected through a needle biopsy or surgical excision. Common biomarkers assessed include HER2, oestrogen receptors (ER), progesterone receptors (PR), PD-L1 for immunotherapy selection, Ki-67 for cell proliferation, and mismatch repair (MMR) proteins such as MLH1 and MSH2 to detect microsatellite instability.

Immunohistochemistry is widely used across almost all solid tumours and haematological malignancies. It is standard practice in breast cancer to evaluate hormone receptor status and HER2 protein expression. It is frequently employed in non-small cell lung cancer, melanoma, colorectal cancer, prostate cancer, stomach cancer, and lymphomas to classify subtypes and evaluate predictive markers.

IHC findings guide treatment choices. Positive oestrogen receptor staining in breast cancer supports endocrine therapy, whilst high HER2 scores indicate benefit from anti-HER2 targeted drugs. High PD-L1 expression can support using immune checkpoint inhibitors. Negative results indicate alternative therapies, such as standard chemotherapy, are more appropriate.