Subcutaneous panniculitis-like T-cell lymphoma.

Subcutaneous panniculitis like T-cell lymphoma derived from α/β T-cells (SPTCL-AB) belongs to the group of primary cutaneous T-cell lymphoma, and it represents less than the 1% of all primary cutaneous T-cell lymphomas. It affects patients in the 4th decade of life (median age of 36 years) with a female preference (male/female ratio 0.5) with 19% of patients being 20 years or younger. It can be sometime complicated by a hemophagocytic syndrome, and patients without hemophagocytic syndrome had a significantly better survival (5-year OS: 91% vs. 46%). Histopathologically, SPTCL-AB is characterized by a lobular lymphocytic panniculitis. Tumor cells distribute between individual adipose lobules, proliferating and forming "rim" and "capping" images, conferring a lace-like appearance at scanning magnification. This is not an entirely disease-specific feature, and can also be seen in other lobular lymphocytic panniculitis, either of inflammatory and neoplastic origin. Tumor cells are phenotypically CD45RO+, βF1+ (a monoclonal antibody able to identify the alpha/beta chain of TCR), CD3+, CD4-, CD8+, and express cytotoxic granules (TIA-1, granzyme and perforin), whereas they show variable deletion of T-cell restricted antigens like CD2, CD5 and CD7. The majority of cases show a monoclonal rearrangement for TCR beta and gamma genes and do not show genomic integration of EBV. The present review will focus on histopathologic, immunophenotypical and molecolare data useful to overcome to a specific diagnosis of SPTCL-AB and to differentiate SPTCL-AB from other lymphomas of T-cell or NK/T cell origin and with benign panniculitidis sharing with SPTCL-AB a predominant lobular lymphocytic pattern of involvement of subcutaneous tissue.