# Atypical presentation of γ/δ mycosis fungoides with an unusual phenotype and SOCS1 mutation

## TL;DR

An 81-year-old man with a long history of skin issues was diagnosed with an aggressive form of T-cell lymphoma with a rare γ/δ+ and CD8+ phenotype and a SOCS1 mutation.

## Contribution

This case report presents a rare γ/δ+ mycosis fungoides with a cytotoxic phenotype and a likely pathogenic SOCS1 mutation.

## Key findings

- The patient's skin tumors showed high metabolic activity and FDG uptake in retroperitoneal lymph nodes.
- Histology revealed a γ/δ+ and CD8+ T-cell lymphoma with a blastic morphology and abnormal immunophenotype.
- Next-generation sequencing identified a likely pathogenic SOCS1 mutation with 72% allele frequency.

## Abstract

Mycosis fungoides is the most frequent subtype of primary cutaneous T-cell lymphomas. The diagnosis is based on a thorough clinic-pathologic correlation, which can, especially in early-stage disease, be challenging due to similarities with several benign skin disorders such as psoriasis and atopic dermatitis. Here, we present a case of an 81-year-old man with a 20-year-long medical history of skin problems treated as psoriasis with limited effect. Since December 2021, the patient experienced worsening of his skin symptoms with rapidly growing tumors and widespread patches and plaques. Positron emission tomography/computed tomography evaluation revealed markedly metabolic activity related to the skin tumors and increased FDG uptake in several retroperitoneal lymph nodes. Histological assessment of skin biopsies demonstrated a highly proliferative T-cell lymphoma with a γ/δ+ and CD8+ cytotoxic phenotype. The morphology of the tumor cells appeared blastic with an abnormal immunephenotype CD3+, CD2−, CD5dim, CD4−, CD8+, CD56−, and CD30−. Next-generation sequencing detected a likely pathogenic SOCS1 mutation with an allele frequency of 72% as well as a STAT3 variant of unknown significance. This case highlights the diagnostic complexity of an indolent skin lymphoma evolving into an aggressive cytotoxic lymphoma.