Acquired aberrant partial CD3 expression in recurrent Epstein-Barr virus-negative solitary plasmacytoma of tonsil

The aberrant expression of specific T-cell maker CD3 in B-cell neoplasms can be a potential diagnostic pitfall leading to a misclassification of cell lineage. Here, we report a case of recurrent solitary plasmacytoma with new aberrant expression of CD3. The neoplastic plasma cells of the recurrent tumor were kappa restricted, positive for CD138, MUM1, negative for CD20, cyclin D1, and Epstein-Barr virus. CD79a was positive in majority of the tumor cells, except for a small focus which was strongly positive for CD3, but negative for other T-cell markers (CD2, CD5, CD7, CD4, and CD8) and CD56. The neoplastic plasma cells of the original tumor were negative for CD3. To the best of our knowledge, only one case of recurrent plasmacytoma with aberrant expression of CD3 has been published, which revealed disease progression in the recurrence. However, we did not observe morphologic evidence of disease progression in our case.