Comparison of T-lymphocyte proliferation in canine epitheliotropic lymphosarcoma and benign lymphocytic dermatoses

The lesions of patch/plaque cutaneous T-cell lymphosarcoma (CTCL) are similar to many benign inflammatory dermatoses, both histopathologically and clinically. In humans, attempts to develop a simple, reliable immunophenotypic technique to differentiate between the malignant and benign dermatoses have been unsuccessful. The purpose of our study was to determine, using a proliferating cell nuclear antigen (PCNA)/CD3 double immunolabelling technique of paraffin-embedded sections, if the rate of T-cell proliferation in canine CTCL was greater than that of other diseases with non-neoplastic lymphocyte epitheliotropism. We selected cases of patch/plaque (PP) and tumour stage CTCL, erythema multiforme (EM) and cutaneous lupus erythematosus (CLE). We did not find a significant difference in the rate of T-cell proliferation in the epithelia nor the superficial dermis between PP-CTCL and EM. Whereas epithelial T-cell proliferation is significantly higher in PP-CTCL than CLE, it is not diagnostically useful because of overlap in the labelling indices.