We now can determine histogenesis of cells, and therefore determine the cell of origin for many of the most difficult tumor cases. In 1985, Gatter et al. convincingly demonstrated the value of immunohistochemistry in a study of 120 cases of malignancy that were difficult to diagnose. The value is indisputable. Consider just one example. Undifferentiated tumors which on testing may be carcinoma, sarcoma, melanoma or lymphoma.
Tumors presenting without a distinctive pattern are always a challenge to pathologists.
To avoid diagnostic errors and incorrect therapy, the pathologist should obtain immunohistochemistry evaluation to at least establish the histogenesis of the tumor. Adenocarcinoma from an unknown primary site. These tumors require a more precise diagnosis to guide therapy. A tumor derived from the pancreas, for example, is treated differently from one derived from the ovary. Adenocarcinoma vs. mesothelioma.