The expression of MUM1 in cutaneous T-cell lymphoproliferative disorders

MUM1 is a member of the interferon regulatory factor family of transcription factors. It is normally expressed in plasma cells, late B cells, and activated T cells, and has been described in several B-cell malignancies. Although its expression has been reported in some T-cell neoplasms, the full range and character of expression have not been explored. We studied 58 cases of T-cell lymphoproliferative lesions, including systemic and cutaneous anaplastic large cell lymphoma, lymphomatoid papulosis (LyP), mycosis fungoides (MF), MF with large cell transformation, and Sezary syndrome (SS). Nearly all cutaneous (515) and systemic anaplastic large cell lymphomas (4/5) were positive for MUM1, mainly in the large cell population. Similarly, 12 of 16 types A and C LyP showed MUM1 reactivity in greater than 50% of the large cells. Focal MUM] staining was seen in 3 type B LyP, mostly in reactive lymphoid cells. All 9 MF with large cell transformation expressed MUM1 in large cells, where it paralleled CD30 expression. In comparison, most MF (11/12) were MUM I negative. Interestingly, all SS cases (8/8) were MUM1 positive, 3 of which demonstrated diffuse staining. There was a significant difference in MUM1 expression between MF and SS groups as well as between MF and large cell transformation of MF groups (P <.001 for both). In summary, MUM1 is not helpful in separating different types of CD30-positive lymphoproliferative disorders. Potentially, MUM1 could serve as an adjunct marker for SS and/or large cell transformation of ME (C) 2008 Elsevier Inc. All rights reserved.