IRF4 Gene Rearrangements Define a Subgroup of CD30-Positive Cutaneous T-Cell Lymphoma: A Study of 54 Cases

The identification of IFN regulatory factor 4 gene (IRF4) translocation in 8 out of 14 cases of cutaneous anaplastic large cell lymphomas (C-ALCLs) (Leukemia, 2009; 23(3):574-80) prompted us to study IRF4 locus status in different cutaneous T-cell lymphoma (CTCL) subtypes. Fluorescence In situ hybridization (FISH) was used with break-apart dual-color probes. Sixty samples from 54 patients were analyzed with 23 C-ALCL, 11 transformed mycosis fungoides (T-MF), 7 lymphomatoid papulosis (LyP), and 13 Sezary syndrome (SS) cases. IRF4 immunostaining was performed in 32 cases. We observed a split FISH signal pattern indicating a translocation at the IRF4 locus in 6 out of 23 C-ALCL (26%) and 2 out of 11 T-MF (18.2%) cases. Extra copies of the IRF4 locus were found in 4 out of 13 SS, 1 out of 11 T-MF, and 1 out of 23 C-ALCL cases, corresponding to either aneuploidy, chromosome 6 trisomy, or 6p partial gain. The IRF4 expression was not correlated with the presence of IRF4 alteration in C-ALCL or T-MF. Interestingly, IRF4 rearrangements define a subgroup of CD30-positive C-ALCL and T-MF cases. Conversely, T-MF cases with IRF4 rearrangements may correspond to the development of C-ALCL in MF patients and not to large cell transformation. Investigation of the biological pathways triggered by IRF4 rearrangements and/or expression in CTCL will provide a biological basis for IRF4-directed therapy.