TOtal Skin Electron Beam Therapy (Low-dose) for Tumor Clone Eradication in Early-stage Mycosis Fungoides

Primary cutaneous T-cell lymphomas are a group of peripheral T-cell lymphomas that primarily involve the skin. Mycosis fungoides (MF) is the most frequent subtype. Most patients with early-stage MF (i.e., patches and plaques of the skin without extracutaneous involvement) have a good prognosis but a subset of patients progress to incurable advanced-stage disease with an overall survival (OS) less than 5 years and an impaired quality of life. We have recently identified the tumor clone frequency in lesional skin (measured by high-throughput sequencing of the TCRB locus) as the most important prognostic factor of progression-free survival (PFS) and OS in a retrospective analysis on 210 patients with early-stage MF (p\<0.001). Phototherapy is a standard therapeutic option in early-stage MF but fails to eradicate the tumor clone from the skin. Low-dose total-skin electron-beam therapy (LDTSEBT, 12 Gy over a 3-week period) has been shown to be safe and highly effective in MF with an 88% overall response rate and a better safety profile compared to standard-dose total-skin electron-beam therapy, in a pooled analysis from 3 phase II trials on 33 patients and a retrospective analysis of 12 patients treated with LDTSEBT. We hypothesize that the use of LDTSEBT is associated with a significantly higher 1-year PFS compared to conventional treatment with phototherapy. Our secondary hypotheses are that LDTSEBT is associated with a higher tumor T-cell clone eradication compared to phototherapy, and improves OS and quality of life in patients with skin-limited MF. The main objective of this study is therefore to prospectively determine if LDTSEBT is associated with a higher 1-year progression-free survival in patients with early-stage mycosis fungoides, compared to conventional treatment with phototherapy. The primary endpoint is PFS at 12 months after study inclusion.