Case report: a case of primary cutaneous diffuse large B-cell lymphoma, leg type with TdT positive in an elderly woman.

BACKGROUND: Primary cutaneous diffuse large B-cell lymphoma, leg type(PCDLBCL-LT) is a rare form of lymphoma that originates from the post-germinal center and typically does not express terminal deoxynucleotidyl transferase(TdT), a marker of immunophenotypic immaturity. CASE DESCRIPTION: A 73-year-old female presented to our hospital with recurrent nodules on her lower limbs, which had persisted for over five years without systemic involvement, accompanied by a gradual increase in TdT expression. Histology revealed diffuse infiltration of centroblasts and/or immunoblasts within the dermis and subcutis, with CD20, CD10, BCL2 and c-MYC expression. Fluorescence in situ hybridization (FISH) showed MYC rearrangement without BCL2/BCL6 alterations, corroborating the diagnosis of TdT-positive PCDLBCL-LT. Following six cycle of R-CHOP chemotherapy, the patient achieved complete remission. A follow-up conducted one year showed no tumor recurrence. CONCLUSION: Our case showed that TdT can be expressed in PCDLBCL-LT, and highlight the importance of a comprehensive analysis of clinicopathology and ancillary testing to avoid misdiagnosis. Additionally, the clinical course of TdT-positive PCDLBCL-LT seems remain relatively favorable. However, further research is still needed on this relationship.