Cytokeratin positive T cell malignant lymphoma.

A high grade T cell malignant lymphoma is described in which weak staining of tumour cells for leucocyte common antigen and T cell markers coexisted with strong positive cytoplasmic staining with the anticytokeratin marker CAM 5.2. This is the first report of non-CD30 positive T cell lymphoma showing cytokeratin positivity. On ultrastructural examination there was no evidence of epithelial differentiation or of accumulation of cytokeratin-type intermediate filaments. The case adds to the range of malignant lymphomas which can, on rare occasions, show cytokeratin positivity. Pathologists should be aware of this potential diagnostic pitfall if inappropriate investigations and therapeutic regimens are to be avoided.