Primary Cutaneous T-Cell Lymphomas Showing Gamma-Delta (γδ) Phenotype and Predominantly Epidermotropic Pattern are Clinicopathologically Distinct From Classic Primary Cutaneous gd T-Cell Lymphomas

Primary cutaneous gamma-delta (gamma delta) T-cell lymphoma is a rare disease that typically involves the dermis and subcutis. Cases of primary cutaneous T-cell lymphomas showing gamma delta phenotype and predominantly epidermotropic pattern (E gamma delta TCL) are not well defined. In this series, cases of primary cutaneous T-cell lymphomas showing gamma delta phenotype were reviewed and classified as predominantly epidermotropic (E gamma delta TCL) when > 75% of lymphoma cells resided in the epidermis or predominantly dermal and/or subcutaneous (DS gamma delta TCL). Clinical, pathologic, and immunophenotypic features were compared in 27 biopsies from 13 patients of E gamma delta TCL and 13 biopsies from 7 patients of DS gamma delta TCL. The lymphoma cells were diffusely positive for CD3 and T-cell receptor (TCR) gamma, mostly positive for granzyme B and TIA-1, variably positive for CD8, CD7, and CD30, and negative for CD4 and TCRb. Two patients with E gamma delta TCL had dissemination to lymph nodes and 1 to the lung; 1 patient with DS gamma delta TCL had gastrointestinal involvement. The median survival of patients with E gamma delta TCL was not reached, and with a median follow-up of 19.2 months, 3/13 died. In contrast, the median survival of patients with DS gamma delta TCL was 10 months, and after a median follow-up of 15.6 months, 5/5 died (P< 0.01). E gamma delta TCL is a rare presentation of cutaneous T-cell lymphoma that can be distinguished from DS gamma delta TCL based on the extent of epidermotropism and has a better prognosis and longer median survival than DS gamma delta TCL. However, although E gamma delta TCL resembles mycosis fungoides clinically and histologically, a subset of E gamma delta TCL is more likely to behave more aggressively than typical mycosis fungoides.