Mycosis fungoides - differentiation from inflammation and detection of circulating tumor cells with the EuroClonality-NGS assay.

Mycosis fungoides (MF) is a rare malignancy characterized by the presence of circulating tumor cells (CTCs) in a subgroup of patients. Reliably distinguishing MF from inflammatory skin conditions (IF) is a challenging task. This study aimed to evaluate the potential benefits of next-generation sequencing (NGS)-based T-cell receptor (TR) rearrangement repertoire analysis for detecting clonal rearrangements in MF and IF. Skin biopsies and blood samples from 33 MF patients (diagnosed according to WHO-EORTC criteria) and 10 IF patients were analyzed using TRB- and TRG-NGS. 27/33 MF patients were early-stage IA (n=19), IB (n=8), and six had advanced stages (IIB, n=5; IIIA, n=1). Analysis applying the standard abundance thresholds identified at least one clonal rearrangement in the skin DNA of 32/33 MF (97%) and 9/10 IF cases (90%). To enhance specificity, an abundance- and distribution-based approach was applied, considering only rearrangements that significantly stood out from the physiological background as clonal (MF 29/33, IF 1/10), allowing for a highly sensitive (88%) and specific (90%) discrimination between MF and IF. CTCs were detected in 11/24 (46%) early-stage and 3/5 (60%) late-stage MF patients. NGS-based TR repertoire analysis is a highly sensitive and specific method for the differential diagnosis of early-stage MF compared to IF, and for the sensitive molecular detection of CTCs.