203 - Defining the Role of Radiotherapy for Indolent, Primary Cutaneous B-Cell Lymphoma - First Results from a Multicenter Registry by the International Lymphoma Radiation Oncology Group (ILROG)

M. Oertel¹, D. Goerlich², V. R. Sim³, S. Morris³, A. Hashmi⁴, M. Levis⁵, C. R. Kelsey⁶, C. R. Weil⁷, M. Chelius⁸, C. Hague⁹, D. E. Roos¹⁰, Y. Kirova¹¹, R. Fietkau¹², P. Fang¹³, A. K. Ng¹⁴, Y. D. Tseng¹⁵, S. A. Terezakis¹⁶, R. T. Hoppe⁴, and H. T. Eich¹; ¹Department of Radiation Oncology, University Hospital Muenster, Muenster, Germany, ²Institute of Biostatistics and Clinical Research University of Muenster, Muenster, Germany, ³Guys and St Thomas NHS Foundation Trust, London, United Kingdom, ⁴Department of Radiation Oncology, Stanford University School of Medicine, Stanford, CA, ⁵Dept. of Oncology, University of Torino, Torino, Italy, ⁶Duke University Medical Center, Department of Radiation Oncology, Durham, NC, ⁷Department of Radiation Oncology, Huntsman Cancer Institute, University of Utah, Salt Lake City, UT, ⁸Department of Radiation Oncology, Hospital of the University of Pennsylvania, Philadelphia, PA, ⁹Clinical Oncology, The Christie NHS Foundation Trust, Manchester, United Kingdom, ¹⁰Royal Adelaide Hospital, Adelaide, SA, Australia, ¹¹Institut Curie, Paris, France, ¹²Department of Radiation Oncology, Universitätsklinikum Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg, Germany; Comprehensive Cancer Center Erlangen-EMN, Erlangen, Erlangen, Germany, ¹³Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, ¹⁴Department of Radiation Oncology, Brigham and Women’s Hospital and Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA, ¹⁵Department of Radiation Oncology, University of Washington/ Fred Hutchinson Cancer Center, Seattle, WA, ¹⁶University of Minnesota: Department of Radiation Oncology, Minneapolis, MN

Purpose/Objective(s): Radiotherapy (RT) is a standard treatment for indolent, primary cutaneous B-cell lymphoma. As various RT-concepts exist comprising different doses, fractionations and techniques, a multicenter registry was established to investigate patterns-of-care, response outcomes, and to guide treatment decisions. Materials/

Methods: The analysis included patients with stage T1/T2 primary cutaneous B-cell lymphoma, either as primary cutaneous marginal zone lymphoma (PCMZL) or primary cutaneous follicle center lymphoma (PCFCL), who underwent RT between 2000 and 2020. Data from twenty participating institutions were collected in a data collection web application database (Vanderbilt University, TN, USA) and analyzed via statistical software.
Results: Overall, 440 patients were included, of which 60.9 % were male with a median age of 56.8 years at diagnosis. Histologically, 37.3 % had PCMZL and 54.1 % had PCFCL. A median of 1 lesion (range: 1-10) with a median size of 2.9 cm (range: 0.1-21 cm) were reported. Previous therapies were delivered in 40.9 % of patients with a complete resection in 8.2 %. RT doses differed between 2.0 and 50.4 Gy (Median: 24.0 Gy) with a median fraction dose of 2.0 Gy (1.5-5.0 Gy). Of these, 51 patients were treated with 4 Gy or less. Overall response rate (ORR) at first follow-up was 77.8 % with a complete response rate (CRR) of 76.4 %, reaching a best response of 95.6 % (CRR: 92 %) after a median of 3.9 months. There was a significant difference in OR and CR between the <=4 Gy and >4 Gy group, respectively (ORR: 90.2 % vs. 97.4 %; p=0.022; CRR: 82.4 % vs. 94.3 %; p=0.005). Erythema only developed after RT >4 Gy (50.5 % of patients with documented values vs. 0.0 %; p<0.001), although grades were predominantly mild to moderate (45.2 % grade 1, 4.6 % grade 2 in the > 4 Gy group). There was a significant difference in freedom from local failure between the = 4 Gy group and patients treated with higher doses (5-year freedom from local failure: 71.8 % vs. 95.4 %; p<0.001), with no difference in overall survival (5-year overall survival 97.1 % vs. 93.7 % p=0.290).
Conclusion: RT is an effective treatment modality for indolent, primary cutaneous B-cell lymphoma. As very low doses (e.g., 4 Gy) led to long-term disease control in ca. 70 % of patients, a response-adapted approach could be further explored with full-dose salvage RT being applied in case of a local failure after 4 Gy. Patient recruitment is still ongoing and final results are to be expected at the ASTRO meeting.