SPTCL : Differential Diagnosis

Subcutaneous panniculitis-like T-cell lymphoma (SPTCL) is a rare cytotoxic T-cell lymphoma involving subcutaneous fat. It is positive for alpha-beta receptor (Beta F1+). Cases that express gamma-delta are classified as cutaneous gamma-delta T-cell lymphoma. SPTCL is seen over a wide age range (median age 36 years). Patients develop solitary or multiple, firm, erythematous/violaceous, deep-seated plaques or nodules without ulceration, usually on extremities or trunk. About 50% of patients have B symptoms (fever, malaise, fatigue, and weight loss). SPTCL is associated with immune dysregulation. Many patients have history of systemic lupus erythematosus (20% of cases) or have received immunomodulation or immunosuppressive therapy. Lupus erythematosus panniculitis (LEP) and SPTCL share clinical and morphologic features. The neoplastic cells are pleomorphic, mostly small to medium-sized with occasional large cells localized to the subcutaneous fat. They have hyperchromatic nuclei, scant cytoplasm, and surround individual adipocytes. Immunophenotype: Positive markers: CD3, CD8, Beta F1, TIA1, granzyme B, perforin; Negative markers: CD4, CD56, gamma-delta T-cell receptor, CD30, EBV. T-cell receptor genes are clonally rearranged. SPTCL is an indolent lesion with favorable prognosis. It remains confined to the skin throughout its clinical course. The 5-yr disease-specific survival rate is 80-90%. Prognosis worsens if hemophagocytic syndrome develops. References:Calonje, E et al (2020). McKee's Pathology of the Skin with Clinical Correlations - 5th Ed. Elsevier. Jaffe, E. S. et al (2017). Hematopathology - Second Edition. Philadelphia, PA. Elsevier. Revised 4th Edition of WHO Classification of Tumors of Hematopoietic & Lymphoid Tissues, 2017.