Immunohistochemical staining was performed on 145 biopsies with a diag
nosis of undifferentiated or poorly differentiated tumor in order to c
lassify them into lymphoid, epithelial, or mesenchymal in origin. It w
as possible to arrive at a histogenetic diagnosis on immunostaining in
85.5% of cases. Immunostaining confirmed the diagnosis in 32.4% and c
ontributed to diagnosis in 53.1%. Malignant lymphoma was the most comm
on diagnosis (35.9%), followed by carcinoma (23.4%). A panel of antibo
dies consisting of anti-common leucocyte antigen (LCA), anti-epithelia
l membrane antigen (EMA), anti-cytokeratin (CK), anti-low to intermedi
ate molecular weight cytokeratin (CAM 5.2), anti-S-100 protein (S-100)
, and anti-vimentin (VM) may resolve, to a large extent, some of the c
ommon diagnostic problems. (C) 1994 Wiley-Liss, Inc.