Immunohistochemistry reveals an increased proportion of MYC‐positive cells in subcutaneous panniculitis‐like T‐cell lymphoma compared with lupus panniculitis

Background Subcutaneous panniculitis‐like T‐cell lymphoma (SPTCL) is a malignant primary cutaneous T‐cell lymphoma that shares significant clinical, histopathologic and immunophenotypic overlap with lupus erythematosus panniculitis (LEP). Methods We performed immunohistochemistry for the MYC oncoprotein on 23 cases of SPTCL (1 CD8 negative) and 12 cases of LEP to evaluate if there are quantitative or qualitative differences in protein expression of this marker in these entities. Results In SPTCL cases, the percentage of all cells that were c‐Myc positive ranged from 0.8% to 16%, with a mean of 5.0% and a median of 4.4%. In contrast, in the LEP cases, the percentage of c‐Myc‐positive cells in the cases ranged from 0.34% to 3.7%, averaged 1.4% and the median was 0.8%. The difference between the means of these 2 diagnostic categories was statistically significant. Fluorescence in situ hybridization performed on 4 cases of SPTCL with a relatively high level of MYC immunohistochemical staining, however, failed to demonstrate evidence of MYC rearrangement or amplification. Conclusions Our work demonstrates that MYC expression levels differ between these 2 histologic mimics and suggests that this important oncoprotein may play a role in the pathogenesis of SPTCL.