Hematologic Cancer

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MO_41_2551 - Response Rates of Nodal Versus Extranodal Follicular and Marginal Zone Lymphomas to Very Low Dose Radiation Therapy of Only 4 Gy

Monday, October 22
10:45 AM - 12:15 PM
Location: Innovation Hub, Exhibit Hall 3

Response Rates of Nodal Versus Extranodal Follicular and Marginal Zone Lymphomas to Very Low Dose Radiation Therapy of Only 4 Gy
K. Chau1, J. C. Yang1, C. Hajj1, M. R. Chelius2, and J. Yahalom1; 1Memorial Sloan Kettering Cancer Center, New York, NY, 2Dartmouth's Geisel School of Medicine, Hanover, NH

Purpose/Objective(s): The use of very low dose radiation therapy (RT) with 4 Gy (“boom-boom”) is an increasingly popular alternative to higher doses for indolent non-Hodgkin lymphomas (NHL) such as follicular lymphoma (FL) and marginal zone lymphoma (MZL). The purpose of this study was to explore whether site of involvement affects initial response and local control with 4 Gy.

Materials/Methods: We retrospectively reviewed medical records of all patients (≥18 years of age) with a diagnosis of FL or MZL who received 2 Gy x 2 fractions between 2006 and 2017 at our institution. All patients had a minimum of 2 months follow-up. One hundred thirty-five patients with 167 irradiated lesions were included for analysis. Initial overall response rate (ORR) was assessed using radiographic scans and/or physical examination for complete response (CR), partial response (PR), and no response (NR), according to NCCN guidelines (version 7.2017). Initial ORR was defined as achieving CR or PR at 2 months post-RT and compared using the chi square test. Freedom from local failure (FFLF) was defined as time from treatment to local failure (LF) and estimated using the Kaplan-Meier method and compared using the log-rank test.

Results: Median age for all patients was 67 years (range: 27–92 years) at the start of RT and 60 (44%) were female. There were 74 patients with 86 lesions (51%) who presented with early stage (I-II). Of the 167 lesions, 112 (67%) were FL, 53 (32%) were MZL, and 2 (1%) were unclear FL vs. MZL. There were 97 (58%) extranodal sites of involvement, 63 (38%) nodal, and 7 (4%) mixed. Specific sites of disease included the peripheral nodes (upper body, n=33; lower body, n=16; extremities, n=3), skin (n=39), central nodes (n=22), soft tissue (n=17), orbit (n=17), parotid (n=14), Waldeyer’s ring/nasopharynx (n=6), breast (n=4), lung (n=4), and other (n=5).

Median follow-up for all patients was 26 months (range: 2–133 months). During initial follow-up, 64% of patients achieved CR and 23% PR. The ORR was 87%. Early stage sites (n=86) had a 93% ORR while advanced stage sites (n=81) had an 80% ORR (p=0.015). Excluding mixed sites from the analysis, extranodal sites had a better ORR than nodal (94% vs 76%, p=0.001). Of nodal sites treated (n=59), peripheral nodal sites had a better ORR than central (84% vs 50%, p=0.008). For the 107 (64%) irradiated lesions that achieved an initial CR, there were 13 LF, and 2-year FFLF was 89%. There was no significant difference in 2-year FFLF for extranodal versus nodal sites (88% vs 90%, p=0.65) nor for central versus peripheral nodal sites (100% vs 88%, p=0.51).

Conclusion: Patients with FL and MZL in this series appeared to have excellent initial ORR to 4 Gy very low dose RT, especially if the site of involvement was extranodal. However, among lesions that achieved an initial CR, there was no significant difference between extranodal and nodal sites in the durability of that CR.

Author Disclosure: K. Chau: None. J.C. Yang: Senior Committee Member; ARRO. M.R. Chelius: None. J. Yahalom: Chairman; ILROG.

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