Expansion
Antibodies against lineage-specific proteins identify a tumour's origin
Expansion
| Marker | Identifies |
|---|---|
| Cytokeratin | Epithelial, so carcinoma |
| Vimentin | Mesenchymal, so sarcoma |
| Desmin, myogenin | Muscle |
| S100 | Melanoma, nerve sheath tumours, Langerhans cells |
| Melan-A, HMB-45 | Melanoma, more specific |
| CD45 (leucocyte common antigen) | Lymphoid |
| CD20 | B cells; CD3 T cells |
| Chromogranin, synaptophysin | Neuroendocrine |
| GFAP | Glial |
| TTF-1 | Lung and thyroid |
| PSA | Prostate |
| CD117 (c-KIT) | GIST |
| Oestrogen and progesterone receptors, HER2 | Breast, and they determine treatment |
| Ki-67 | Proliferation index |
The typical approach to a carcinoma of unknown primary is a panel: first establish the broad lineage (cytokeratin, CD45, S100, vimentin), then narrow with organ-specific markers.
Immunohistochemistry has become predictive as well as diagnostic: HER2 and hormone receptors determine breast cancer therapy, PD-L1 predicts checkpoint inhibitor response, and mismatch repair protein loss identifies Lynch syndrome and predicts immunotherapy benefit.