Knowledge Base

Expression of the pan B-cell marker CD20 by T-cell lymphoproliferative disorders is exceedingly rare. We present a 52-year-old man with a unilesional cutaneous CD20 T-cell lymphoproliferative disorder. Multispectral imaging analysis of CD3-CD20 double-stained lesional tissue sections allowed (1) the visualization of double-positive T lymphocytes in situ with sensitivity superior to that of conventional immunohistochemistry and (2) the quantitative assessment of marker coexpression. Here, 23% of CD3 signals in the patient's lesion were also CD20, whereas 38% of CD20 signals were also CD3. In contrast, both parameters were below 1% in the tonsil control. Overall, the percentage of double-positive cells in lesional skin was 35%, although only 0.4% of such cells were detected in the tonsil. This is the first demonstration of aberrant CD20 expression by skin-infiltrating T cells using multispectral imaging.