Frequency and prognostic value of cutaneous molecular residual disease in mycosis fungoides: a prospective multicentre trial of the Cutaneous Lymphoma French Study Group

{Background Monoclonal T-cell receptor (TCR) rearrangement is detected in 57-75% of early-stage mycosis fungoides (MF) at diagnosis. A retrospective study showed molecular residual disease (MRD) in 31% of patients in complete clinical remission (CR) after 1 year of treatment. Objectives To confirm the frequency of MRD at 1 year and to determine its prognostic value for further relapse. Methods Patients with T1-, T2-or T4-stage MF were prospectively included in this multicentre study. At diagnosis, clinical lesions and healthy skin were biopsied. After 1 year of topical treatment, previously involved skin of patients in CR was biopsied for histology and analysis of TCR-gamma gene rearrangement. The results were compared with the clinical status each year for 4 years. Results We included 214 patients, 133 at T1, 78 at T2 and three at T4 stage. At diagnosis, 126 of 204 cases (61.8%) showed TCR clonality in lesional skin. After 1 year, 83 of 178 patients (46.6%) still being followed up were in CR and 13 of 63 (21%) showed MRD. At 4 years, 55 of 109 patients (50.5%) still being followed up were in CR and 44 of 109 (40.4%) were in T1 stage. MRD did not affect clinical status at 4 years (CR vs. T1/T2