C-MYC expression analysis by immunohistochemistry in cases of subcutaneous panniculitis T-cell lymphoma and lupus panniculitis

Background Subcutaneous panniculitis-like T-cell lymphoma (SPTCL) is an uncommon cutaneous T-cell lymphoma commonly seen in middle-aged females. Lupus panniculitis (LP) is a close differential of SPTCL and the clinical, histological, and immunohistochemical profiles of these two mimics fairly overlap, making differentiation challenging. Aim This study attempts to see if there is any difference in the cellular myelocytomatosis oncogene (c-MYC) expression of both entities. Methods From the electronic archive of the Department of Histopathology, all cases of SPTCL and LP diagnosed between 2015 and 2022 were retrieved. The c-MYC IHC was performed on nine SPTCL biopsies available from seven patients and eleven LP cases. The percentage of c-MYC-positive cells was quantified and compared between the two groups. Results The mean age of patients with SPTCL and LP was 27.7 years (range: 10-50 years) and 35.9 years (range: 18-62 years), respectively. The c-MYC positivity was higher in cases of SPTCL, ranging from 0.5-22% with a mean of 10.6% and a median of 9%. The LP cases had a lower positivity rate with a range of 0-8% with a mean of 1.9% and a median of 1.2% (p value 0.0005). Additionally, c-MYC positivity was more pronounced in areas with fat entrapment, i.e., in atypical lymphocytes rimming individual fat cells with apoptotic debris. Limitation The limitations include small sample size, absence of FISH studies in all cases and non availability of T cell receptor analysis. Conclusion This study highlights the importance of the IHC of c-MYC in diagnosing SPTCL vs. LP. The higher percentage of c-MYC-positive atypical cells in SPTCL suggests that this oncoprotein may have a significant involvement in the pathogenesis of SPTCL.