An unusual pattern of lymph node involvement in mycosis fungoides simulating neoplastic follicles.

We describe an unusual pattern of lymph node involvement in a case of mycosis fungoides. The neoplastic proliferation formed pale nodules composed of small, irregular lymphoid cells, features that, on routine paraffin sections, suggested neoplastic follicles and a B-cell phenotype. The correct diagnosis was established by immunohistochemical studies that demonstrated a T-cell phenotype. Polymerase chain reaction for rearrangement of the T-cell receptor gamma gene confirmed that the proliferation was monoclonal. This case demonstrates that both architectural pattern and cytologic features may be unreliable in predicting immunologic phenotype. Immunologic marker studies and careful attention to the clinical history are vital to classify lymphoproliferative disorders correctly.