Immunohistochemistry (IHC) Markers — Overview

IHC uses antibodies against specific cellular antigens to stain tissue sections, helping classify tumors and other tissues that look ambiguous on routine H&E staining. Here's a breakdown by major category (Robbins Pathologic Basis of Disease, p. 349-353):

1. Lineage/Category Markers (for undifferentiated tumors)

When a tumor is too poorly differentiated to classify by morphology alone, panels distinguish carcinoma vs. lymphoma vs. melanoma vs. sarcoma:

Marker	Lineage indicated
Cytokeratins (pan-CK, CK7, CK20, AE1/AE3)	Epithelial (carcinoma)
Vimentin	Mesenchymal (sarcoma)
Desmin	Muscle origin
CD45 (LCA)	Hematopoietic/lymphoid neoplasms
SOX10, S100, Melan-A, HMB-45	Melanoma

2. Site-of-Origin Markers (for metastases of unknown primary)

Used when a metastasis is found but the primary tumor isn't obvious:

PSA - prostate carcinoma
Thyroglobulin, TTF-1 - thyroid (TTF-1 also positive in lung adenocarcinoma)
CDX2 - colorectal
GATA3, mammaglobin, GCDFP-15 - breast
CK7/CK20 patterns - help narrow GI vs. lung vs. urothelial vs. ovarian origin

3. Lymphoid/Hematopoietic Panel

CD45 - pan-leukocyte
CD20, CD79a, PAX5 - B-cells
CD3, CD5 - T-cells
CD15, CD30 - Hodgkin (Reed-Sternberg cells)
CD34, MPO - myeloid/blast lineage

4. Prognostic/Therapeutic (Predictive) Markers

These directly guide treatment decisions:

ER/PR (estrogen/progesterone receptors) - breast cancer; positivity predicts response to antiestrogen therapy and confers better prognosis
HER2 (ERBB2 product) - breast (and gastric) cancer; strong staining identifies candidates for anti-HER2 antibody therapy (often confirmed with FISH for gene amplification)
ALK - identifies ALK-fusion-positive lung cancers and lymphomas, indicating eligibility for ALK inhibitors
PD-L1 - predicts response to checkpoint inhibitor immunotherapy
Ki-67 - proliferation index, prognostic across many tumor types

5. Neuroendocrine Markers

Synaptophysin, chromogranin, CD56 - identify neuroendocrine tumors (carcinoids, small cell carcinoma, pancreatic NETs)

Example: Anti-cytokeratin stain confirming epithelial origin

Anti-cytokeratin immunoperoxidase stain of a carcinoma

This is a broad topic - IHC panels are typically tailored to a specific clinical question (e.g., "carcinoma of unknown primary," "lymphoma subtyping," "spindle cell tumor workup," "breast cancer receptor status"). If you have a specific tumor type or diagnostic scenario in mind, I can give you the exact panel and interpretation used for that workup.

This is a shared conversation. Sign in to Orris to start your own chat.