Radiotherapy dose-response of mycosis fungoides with large cell transformation

Mycosis fungoides (MF) is the most prevalent subtype of primary cutaneous T-cell lymphoma. Large cell transformation of MF (LCTMF) is rare and confers a poor prognosis. Radiotherapy (RT) is an effective local treatment for LCTMF; however, dose-response data are limited.

Eligibility for this retrospective study required biopsy-proven LCTMF with clinico-pathological correlation, diagnosed 1/1/1990-1/10/2021, and managed at Peter MacCallum Cancer Centre.

83 patients were eligible. Median age was 68 years, 63 (76 %) patients had cutaneous-only LCTMF at time of diagnosis. Median follow-up was 8.0 (95 % CI: 6-11) years. Details of 155 irradiated LCTMF lesions (from 49 patients) were available: 150 cutaneous, 5 extra-cutaneous. For cutaneous LCTMF, median equivalent dose in 2.0 Gy per fraction (EQD2, α/β of 10) was 30.6 (range, 4.7-46.3) Gy. Dose-response data were available for 141 cutaneous LCTMF lesions. Overall response rate (ORR) was 94 % (60 % complete response (CR), 35 % partial response). For cutaneous lesions treated with >12.0 Gy, ORR was 100 %. Increasing doses of RT were associated with greater CR rates: doses >36.0 Gy achieved 100 % CR rate. 22 (27 %) patients had unifocal cutaneous-only LCTMF and were treated with local RT-alone, median EQD2 36.0 Gy (range, 17.3-46.3 Gy). CR rate was 100 %. 9 (41 %) patients remained relapse-free (median follow-up, 3.2 years). Only 1 patient experienced infield-only recurrence at first relapse.

LCTMF is radio-responsive, with EQD2 >12.0 Gy associated with 100 % ORR. Dose-response was observed, with EQD2 >36.0 Gy achieving 100 % CR rate. For unifocal cutaneous LCTMF, RT-alone achieved excellent infield control with possible curative potential in a proportion of patients.