Primary Cutaneous Gamma/Delta T-Cell Lymphoma: Report of Three Cases with Heterogeneous Prognosis and Unusual Findings

Summary: Primary cutaneous gamma/delta T-cell lymphoma (PCGDTCL) is a rare lymphoma subtype traditionally viewed as aggressive. Recently, a gamma/delta mycosis fungoides (G/D-MF) variant has been identified as indolent, with a better prognosis, though some cases may progress to classic PCGDTCL. We report the clinical, pathological, and molecular findings of three cases, highlighting diagnostic challenges and variable clinical courses. An 88-year-old male with erythematous plaques was initially diagnosed with CD8+ mycosis fungoides. Over six years, the disease progressed to ulcerated nodules diagnosed as G/D-MF with transition to PCGDTCL. An unusual finding was that the neoplastic T-cells co-expressed CD20 and showed IGH and IGK clonal rearrangements. The patient succumbed to the disease. A 68-year-old male with rheumatoid arthritis presented with an ulcerated rash diagnosed as tumid lupus. Over four years, the disease progressed to PCGDTCL. The patient remains stable. A 60-year-old male with erythematous patches was initially diagnosed with mycosis fungoides, later progressing to nodular tumors identified as G/D-MF. The patient remains stable. These cases highlight the diagnostic complexities of PCGDTCL, particularly the G/D-MF subtype, supporting the concept of a heterogeneous disease spectrum with varied clinical outcomes.