3347 - The Impact of Standard vs. Hypofractionated Total Skin Electron Beam Therapy (TSE) on Cytopenias in Mycosis Fungoides/Sezary Syndrome (MF/SS)

M. Chelius¹, L. Cohen², C. Jiang³, J. Baron¹, J. Mallon⁴, A. Tierney⁵, H. G. Hubbeling³, N. M. Hossain⁶, A. Rook², J. Villasenor-Park², S. Samimi², E. Kim², J. P. Plastaras⁷, S. Barta⁸, and M. J. LaRiviere⁷; ¹Department of Radiation Oncology, Hospital of the University of Pennsylvania, Philadelphia, PA, ²Department of Dermatology, Hospital of the University of Pennsylvania, Philadelphia, PA, ³Department of Radiation Oncology, University of Pennsylvania, Philadelphia, PA, ⁴Hospital of the University of Pennsylvania, Philadelphia, PA, ⁵Biostatistics Analysis Center, Center for Clinical Epidemiology and Biostatistics, Perelman School of Medicine, University Pennsylvania, Philadelphia, PA, ⁶Department of Medicine, Division of Hematology/Oncology, Hospital of the University of Pennsylvania, Philadelphia, PA, ⁷Department of Radiation Oncology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, ⁸Department of Medicine, Division of Hematology/Oncology, University of Pennsylvania, Philadelphia, PA

Purpose/Objective(s): Low-dose TSE can rapidly attain cutaneous control in MF/SS, though duration is limited. Hypofractionated (HF) TSE is gaining interest due to shorter treatment schedules and potential for decreased lymphotoxicity. However, the impact of standard fractionation (SF) or HF TSE on hematologic parameters is poorly characterized, and in advanced MF/SS cytopenias may preclude or delay initiation of critical systemic therapy. Here, we compare hematologic toxicities among SF and HF regimens. Materials/

Methods: From 2015-2023, 111 patients (pts) underwent 121 courses of SF or HF TSE. SF was defined as 1 Gy/fraction totaling 12 Gy, and HF as 1.5-2 Gy/fraction totaling 12 Gy. Complete blood counts were recorded at the following intervals: 1 month (mo) pre-RT (3 mo pre-RT when 1 mo data were unavailable), -1 week through 1 mo post final RT fraction, >1-2 mo, and >2-3 mo. Toxicities were graded per CTCAEv5, with grade 1-2 categorized as low grade (LG) and 3-4 as high grade (HG).
Results: There were 104 SF and 17 HF courses of TSE, with median follow up of 21 mo (0-86). Cohorts were well balanced other than ECOG performance status (PS) 0-1 vs. 2-4, with poorer PS in the HF group (p=0.03). At baseline, 16% had leukopenia (1% HG), 69% had anemia (all LG), 11% had thrombocytopenia (all LG), 45% had lymphopenia (17% HG), and 8% had neutropenia (1% HG). There were no significant differences in pre-TSE cytopenias between cohorts. Cytopenia rates post TSE did not differ between cohorts (see Table 1). HG lymphopenias were observed at all time points among the SF and HF cohorts: pre-TSE 16% vs 25%, -1 week-1mo 23% vs 33%, >1mo-2mo 19% vs 29%, and >2-3mo 11% vs 20% (p>0.05). Best cutaneous response rates did not significantly differ between SF and HF groups: CR 18% vs 18%, PR 73% vs 77%, SD 5% vs 0%, POD 1% vs 6%, unknown 3% vs 0%, respectively (p=0.5). Median time to best response was 1.9 vs 2.8 months respectively (p=0.2). Median time to disease progression was 5.8 vs 6.4 months, respectively (p=0.8).
Conclusion: MF/SS pts presenting for TSE have high rates of cytopenias at baseline which persist following TSE. Cytopenias following TSE and response rates did not differ between SF and HF regimens. Thus, TSE for cutaneous control using SF or HF appears unlikely to prevent subsequent initiation of systemic therapy due to hematologic toxicity.

Abstract 3347 – Table 1

	(-)1wk - 1mo post RT			>1mo - 2mo post RT			>2mo - 3mo post RT
	SF	HF		SF	HF		SF	HF
	n=56 %	n=9 %	p	n=47 %	n=7 %	p	n=44 %	n=5 %	p
Leukopenia	29	33	0.7	34	43	0.7	36	20	0.7
Anemia	75	78	1.0	75	100	0.3	70	80	1.0
Thrombocytopenia	20	11	1.0	13	43	0.1	18	20	1.0
Lymphopenia	66	66	1.0	51	13	0.1	45	40	1.0
Neutropenia	16	22	0.6	17	29	0.6	34	0	0.3