203 - Clinical Factors Associated with Response to Low-Dose Total Skin Electron Beam Therapy: A Multi-Institutional Study By ILROG
Presenter(s)
J. S. Chiang1, J. R. Gunther2, S. Kol2, S. Yost3, E. Ruan4, M. Abouegylah5, K. Elsayad6, L. Nygaard7, L. Specht7, C. Rodriguez-Russo8, C. O'Driscoll9, M. Chisam10, N. J. Park1, M. Khodadoust11, Y. Kim11,12, C. R. Kelsey10, R. Tao4, D. K. Gaffney3, D. R. Steike13, and M. S. Binkley1; 1Department of Radiation Oncology, Stanford University, Stanford, CA, 2Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, 3Department of Radiation Oncology, Huntsman Cancer Institute, University of Utah, Salt Lake City, UT, 4Department of Radiation Oncology, Mayo Clinic, Phoenix, AZ, 5Department of Clinical Oncology, Alexandria University, Alexandria, Egypt, 6Department of Radiotherapy and Radiation Oncology, Marburg University Hopsital, Marburg, Germany, 7Department of Oncology, Rigshospitalet, Copenhagen, Denmark, 8Department of Radiation Oncology, University of Minnesota, Minneapolis, MN, 9Department of Radiation Oncology, University of Minnesota Medical School, Minneapolis, MN, 10Department of Radiation Oncology, Duke University Medical Center, Durham, NC, 11Department of Medicine, Division of Oncology, Stanford Cancer Institute and Stanford University, Stanford, CA, 12Department of Dermatology, Stanford University School of Medicine, Stanford, CA, 13Department of Radiation Oncology, University Hospital of Muenster, Muenster, Germany
Purpose/Objective(s):
Total skin electron beam therapy (TSEBT) is an established skin-directed therapy for patients with mycosis fungoides (MF) and Sézary syndrome (SS), yet contemporary data characterizing clinical outcomes across diverse fractionation strategies are limited. We sought to evaluate response and durability of TSEBT in a large multi-institutional cohort of patients with MF/SS.Materials/Methods:
We retrospectively included patients with pathologically confirmed MF/SS treated with TSEBT across 10 institutions. Demographic, disease, and treatment variables were collected. Clinical response was categorized as complete response (CR), partial response (PR), stable disease, or progressive disease (PD) based on documented clinical assessment. Date of best response was defined as the first post-treatment evaluation meeting criteria, and duration of response as the time from completion of TSEBT to PD. Overall response rate (ORR) was defined as the combined proportion of patients achieving PR or CR. Progression-free survival (PFS) and overall survival (OS) were estimated using Kaplan-Meier methods. Multivariable logistic regression analysis (MVA) was used to identify prognostic variables for CR and ORR.Results:
We identified 498 patients with median age at diagnosis of 60 years (IQR=48-71) and median pre-TSEBT modified severity-weighted assessment tool score of 38.5 (IQR=20-74). Median follow-up was 23 months (IQR=10.1-51.8). 427 received <16 Gy (range 8-16 Gy) as first course TSEBT (85.7%), followed by 44 (8.8%) receiving TSEBT prior to bone marrow transplant, and finally 25 (5.0%) received >20 Gy as first TSEBT. Focusing on those receiving <16 Gy, the ORR was 87.5%, and CR was 26.7%. Median fraction size was 2.0 Gy (IQR=1.2-2.0); 45.6% and 8.7% of patients received fraction sizes of 2 Gy and >2 Gy, respectively. Median time to best response was 1.4 months (IQR=0.48-2.88) with median duration of response of 5.4 months (IQR, 3.36-11.04). The 2-year PFS and OS for those receiving <16 Gy was 56.8% and 81.6%, respectively; nearly all had only cutaneous progression (97.7%). Among patients treated with =16 Gy in MVA, after adjusting for age, gender, large-cell transformation, and clinical stage, non-Caucasian race was associated with lower odds of CR (OR 0.38; 95% CI, 0.16-0.82; p=0.018) and equivalent ORR; CR rates were 44% in Caucasian patients, 2% in Black patients, and 32% in patients reporting other races. There was no difference in ORR by fraction size. CR was observed in 1 of 52 Black patients, compared to 98 of 319 non-Black patients, corresponding to an unadjusted Fisher’s exact OR of 0.044 (95% CI, 0.001-0.267).Conclusion:
In the largest cohort of patients receiving TSEBT for MF/SS to date, we observe very high ORR (87.5%) to lower doses of TSEBT independent of fraction size. Black patients had a significantly lower response to low dose TSEBT, warranting further investigation into contributing biologic and social factors as well as optimizing clinical management for these patients.