When differentiating tumor origin, pathologists frequently exploit immunohistochemical profiles to achieve a tissue diagnosis.14,15 The basic immunohistochemistry panel delineates cancer cell lineage, using antibodies against leukocyte common antigen (LCA) for lymphoma, S100 and MART-1 for melanoma, cytokeratins such as AE1/AE3 and CAM5.2 for carcinoma, and vimentin for sarcoma. The gene discussed is PTPRC; the disease is cancer.