Citations

e19501 Background: Relapsed and/or refractory (R/R) disease is observed in patients who receive CD19 targeting chimeric antigen receptor (CAR)-T cells to treat B-cell lymphoid leukemias and lymphomas. We generated a novel CAR, MC10029 that targets B-cell activating factor receptor (BAFF-R) to address this unmet medical need. Methods: We engineered a second-generation BAFF-R CAR (MC10029 CAR). The construct includes the single chain variable fragment (scFv) of our newly developed BAFF-R antibody with CD28 costimulatory and CD3ζ signaling domains. We confirmed MC10029 CAR-T cell antigen-specific activation with in vitro degranulation assays and a direct cytolytic assay. We used BAFF-R positive leukemia and lymphoma cell lines in both in vitro and in vivo models to further characterize MC10029 CAR-T cells, and finally, we enriched tumor primary cells from chronic lymphocytic leukemia (CLL) patients as a target for MC10029 CAR-T cells. In preparation for our Phase I clinical trial, we have manufactured three batches of CAR-T cells using a MC10029-encoding lentiviral vector produced under GMP conditions. The production batches of MC10029 CAR-T cells were evaluated for product quality with Viability, Identity and Potency as well as Safety from adventitious viral agents. Antigen specific cytotoxicity of the MC10029 CAR-T cells was confirmed using our standard degranulation assay. Results: MC10029 CAR-T cells elicited in vitro antigen-specific cytotoxicity against Nalm-6 cells, Z138 cells, MEC-1 cells, and a CD19 knock out Nalm-6 model designed to mimic CD19-negative R/R disease. We demonstrated in vivo antitumor effects of MC10029 CAR-T cells in NSG mice challenged with these same cell lines. We showed cytotoxicity of MC10029 CAR-T cells against CLL patients’ tumors. We also showed our quality control results to highlight our clinical trial trajectory. Conclusions: Novel MC10029 CAR-T cells showed broad utility against BAFF-R positive B-cell lymphoid malignancies in a series of in vitro, in vivo, and ex vivo models. With these robust data, we have moved forward to generate clinical grade MC10029 CAR-T cells using cGMP manufacturing and quality protocols in preparation of a MC10029 CAR-T cell Phase I clinical trial.

TPS7587 Background: Covalent (c) Bruton tyrosine kinase inhibitors (BTKi) have transformed the management of MCL, but these agents are not curative. cBTKi share pharmacologic liabilities (e.g., low oral bioavailability, short half-life), which collectively may lead to suboptimal BTK target coverage especially in rapidly proliferating tumors with high BTK protein turnover such as MCL, which can manifest as acquired resistance to BTKi. Pirtobrutinib, a highly selective, non-covalent (reversible) BTKi, has favorable oral pharmacology that enables continuous BTK inhibition throughout the dosing interval regardless of intrinsic rate of BTK turnover. In the phase 1/2 BRUIN study, pirtobrutinib demonstrated promising durable overall response rates and was well tolerated in patients (pts) with MCL regardless of prior therapy (including cBTKi), number of prior lines of therapy, or reason for prior cBTKi discontinuation. Pirtobrutinib was approved by the FDA in January 2023 for R/R MCL after 2 prior lines of therapy including a BTKi. The objective of this study is to establish whether pirtobrutinib is superior to investigator’s choice of cBTKi in pts with previously treated, BTKi naïve MCL. Methods: BRUIN MCL-321 (NCT04662255) is a randomized, open-label, global phase 3 study comparing pirtobrutinib monotherapy versus investigator’s choice of cBTKi monotherapy (ibrutinib, acalabrutinib, or zanubrutinib) in pts with previously treated, BTKi naïve MCL. Approximately 500 pts will be randomized 1:1 and stratified by sMIPI risk (low/intermediate vs high), comparator BTKi (ibrutinib vs acalabrutinib/zanubrutinib), and number of prior lines of therapy (1 vs ≥ 2). Enrollment for this study is ongoing. Adults with a diagnosis of MCL who have received ≥ 1 prior line of systemic therapy for MCL and are BTKi naïve are eligible. Pts must have measurable disease by imaging per Lugano criteria and have progressed on or relapsed following the most recent line of therapy. A history of current or prior CNS involvement, significant cardiovascular disease, stroke or intracranial hemorrhage within 6 months of randomization, and autologous stem cell transplant (SCT), allogeneic SCT or chimeric antigen receptor (CAR) T-cell therapy within 60 days of randomization are key exclusion criteria. Progression-free survival (PFS) per Lugano criteria assessed by an independent review committee is the primary endpoint. Overall response rate, duration of response, investigator-assessed PFS per Lugano criteria, overall survival, event-free survival, time to treatment failure, time to next treatment, PFS2 (time from randomization to disease progression on next line of treatment or death from any cause), safety and tolerability, and pt reported outcomes are secondary endpoints. Clinical trial information: NCT04662255 .

TPS7583 Background: Covalent (c) Bruton tyrosine kinase inhibitors (BTKi) have reshaped the treatment landscape for chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) and are now often used as initial therapy. The MURANO study established 2-year fixed duration venetoclax plus rituximab as a standard of care regimen for patients with relapsed or refractory CLL/SLL. However, its efficacy has not been formally assessed in CLL/SLL patients treated with a cBTKi, a common setting where this regimen is used in contemporary practice. Pirtobrutinib, a highly selective, non-covalent (reversible) BTKi, inhibits both wildtype and C481-mutant BTK with equal low nM potency, and has favorable oral pharmacology that enables continuous BTK inhibition throughout the dosing interval regardless of intrinsic rate of BTK turnover. In the phase 1/2 BRUIN study, pirtobrutinib demonstrated promising durable overall response rates (ORR) and was well tolerated in patients with pre-treated CLL/SLL regardless of prior therapy (including cBTKi), number of prior lines of therapy, BTK C481 mutation status, or reason for prior cBTKi discontinuation. The study's objective is to assess the superiority of adding time-limited pirtobrutinib to the MURANO regimen, hypothesized to prolong disease control in a largely BTKi-pretreated population. Methods: BRUIN CLL-322 (NCT04965493) is a randomized, open-label, global, phase 3 study comparing time-limited pirtobrutinib (200mg QD) plus venetoclax and rituximab versus venetoclax and rituximab in previously treated CLL/SLL patients. Approximately 600 patients, 80% who have been previously treated with cBTKi, will be randomized 1:1 and stratified by del(17p) status (yes/no) and prior BTKi experience (discontinuation due to progressive disease vs due to other reasons vs no prior BTKi exposure). Eligible patients are adults diagnosed with CLL/SLL and require therapy per iwCLL 2018 criteria who have received prior therapy that may or may not include a cBTKi. There are no restrictions on the number of lines of prior therapy. Key exclusion criteria include CNS involvement by CLL/SLL, Richter transformation at any time, prior BCL2 inhibitor or non-covalent BTK inhibitor, or a history of either allogeneic or autologous stem cell transplant, or chimeric antigen receptor T-cell therapy within 60 days prior to randomization. The primary endpoint is progression-free survival (PFS) per iwCLL criteria assessed by an independent review committee. Secondary endpoints include investigator assessed PFS, ORR, overall survival, time to next treatment, event-free survival, safety and tolerability, and patient-reported outcomes. Enrollment is ongoing for patients previously treated with BTKi and completed for BTKi naïve patients. Clinical trial information: NCT04965493 .

7577 Background: Prior research has consistently shown that patients with chronic lymphocytic leukemia (CLL) have an ~2-fold increased risk of developing melanoma compared to controls. MBL is a common condition affecting 8-10 million adults over the age of 40 years in the United States and is a precursor to CLL. Little is known about the association between MBL and melanoma. Herein, we evaluated the risk of incident melanoma in a large cohort of individuals screened for MBL. Methods: Participants from the Mayo Clinic Biobank who had no prior history of hematologic malignancy, were 40 years or older, were residents of counties surrounding Mayo Clinic, and who provided blood samples between 7/2009 and 4/2022 were included in the study. Peripheral blood mononuclear cells were screened for MBL using highly sensitive eight-color flow cytometry. Individuals with MBL were classified as CLL-like MBL (CD5+, CD20dim) or atypical MBL (CD5+, CD20+) based on immunophenotypes, and also classified as low-count MBL (LCMBL) or high-count MBL (HCMBL) based on whether the percent clonal B-cell count was < 85% or ≥85%, respectively. Diagnosis of melanoma was ascertained using ICD codes and review of the electronic health records. All individuals were followed from date of sample upon which MBL screening was performed to the earliest of incident melanoma, loss to follow-up, withdrawal from the study, or September 30, 2022. We used Cox regression to estimate hazard ratios (HR) and 95% confidence intervals (CI), adjusting for age, sex, and history of melanoma in previous 5 years. Results: A total of 7,334 participants were screened for MBL, of which 1,151 (16%) individuals had MBL. Among those with MBL, 1,107 (96.2%) had CLL-like MBL and 1098 (95.4%) had LC MBL. The median age at entry into the MBL screening cohort was 67 years (range 40-101) and 37% were male; individuals with MBL were older (median age 72 vs 65 years) and male (49% vs 35%). After a median follow-up of 2.9 years (range 0-13.2), 121 of the 7,334 (1.6%) participants developed incident melanoma after the date of MBL screening. The 10-year cumulative incidence of melanoma among individuals with MBL was 7.8% (95% CI 4.5-13.5%) compared to 3.4% (2.7-4.4%) in those who screened negative for MBL. After adjusting for age, sex, and history of prior melanoma, we found a 1.81-fold increased risk of incident melanoma (95% CI 1.19-2.76) among individuals with MBL. The increased risk of melanoma persisted when the analysis was restricted to individuals with LCMBL (HR = 1.84; 95% CI 1.21-2.82). Conclusions: In the largest MBL screening cohort to date, we found that LCMBL, a common condition, was associated with an 84% elevated risk of melanoma, similar to the ~2-fold increased risk observed in patients with CLL. These data, together with our prior findings of a heightened risk of serious infections and lymphoid malignancies, suggest that individuals with LCMBL are at increased risk for adverse health outcomes.

7575 Background: Extranodal natural killer/T-cell lymphoma (ENKTL), nasal type, is a rare and aggressive Epstein-Barr virus driven lymphoma, which is most prevalent in East Asia and Latin America. There have been very few large studies outside of Asia. Therapeutic and survival outcomes have not been well characterized in the US. Methods: The National Cancer Database was queried for patients who were diagnosed at aged ≥18 years between 2004 and 2019. Patients who were lost to follow-up were excluded. Kaplan-Meier and multivariate Cox regression analyses were performed. Results: The cohort consists of 2,036 evaluable patients with 68% males, 74% Caucasian, 22% Hispanic Caucasian and 9% African American. The median age at diagnosis was 54 (18-90) years. The median follow up was 71 months (95% CI 66.8-75.7). Early-stage disease (I and II) was reported in 64% while advanced stage disease (III and IV) constituted 36%. Treatment groups include chemotherapy alone (29%), radiation alone (10%), combined modality therapy (CMT-chemoradiation) (42%). The median overall survival (OS) for the whole cohort was 27 months (95% CI 20.6-33.7). Median OS was better in patients with early stage compared to advanced stage disease (90 vs. 6 months, P < 0.001). Among therapeutic groups in early-stage disease, CMT (N = 616) had significantly better median OS than radiation alone (N = 152) or chemotherapy alone (N = 168) (194 vs. 34 vs. 14 months, P < 0.001). No significant difference was seen between radiation alone and chemotherapy alone (P = 0.617). Among patients treated with CMT, chemotherapy-first CMT (N = 134) had better OS than radiation-first CMT (N = 347) (median OS not reached vs. 194 months, P = 0.017). In the advanced stage disease, chemotherapy-treated patients (N = 418) had better median OS compared to patients who did not receive chemotherapy (N = 103) (7.6 vs 1.3 months, P < 0.001). Among patients who received chemotherapy, patients consolidated with SCT (N = 59) had better median OS compared to the patients who received chemotherapy only (N = 353) (63 vs 6 months, P < 0.001) In multivariate analysis, factors associated with worse OS were age (HR 1.021 95% CI 1.015-1.026; P < 0.001) and B-symptoms (HR 1.463 95% CI 1.276-1.678; P < 0.001). Whereas factors associated with better OS were early stage (HR 0.450 95% CI 0.387-0.524, P < 0.001), radiation therapy (HR 0.526 95% CI 0.458-0.603, P < 0.001) and chemotherapy (HR 0.546 95% CI 0.473-0.630, P < 0.001). Conclusions: The study represents one of the largest studies on ENKTL in the US. Early-stage disease is highly curable with CMT with chemotherapy-first sequencing being superior to radiation-first sequencing. Advanced stage disease is associated with extremely poor prognosis overall but is associated with a significant improvement in OS with consolidative SCT with possible role of consolidative RT in advanced stage.

7569 Background: B-cell lymphoma 2 inhibitors (BCL-2i) are well tolerated and effective in treating B-cell lymphoproliferative disorders such as CLL. Investigational agent lisaftoclax is a novel, oral, highly selective and potent BCL-2i. Preclinical data show a strong synergistic effect of lisaftoclax plus ibrutinib in an ibrutinib-insensitive PDXWM1 model. Methods: This global, open-label, multicenter study evaluates the safety and efficacy of lisaftoclax alone and combined with ibrutinib or rituximab in pts with WM. Pts were enrolled in 3 arms: Arm A (lisaftoclax), BTKi-resistant/intolerant pts; Arm B (lisaftoclax plus ibrutinib), treatment-naïve pts; and Arm C (lisaftoclax plus rituximab), BTKi-naïve relapsed/refractory pts. Lisaftoclax was escalated from 400 to 1,200 mg using a modified toxicity probability interval design. A 3-day ramp-up was used for pts at high TLS risk. Primary objectives were pharmacokinetics (PK), safety, and efficacy assessments; responses were assessed per IWWM criteria. Results: As of January 25, 2023, 46 pts were enrolled (Arm A [n = 14]; up to 1,000 mg; Arm B [n = 24]; up to 1,200 mg; Arm C [n = 8]; up to 800 mg). Baseline characteristics are shown in the table. Median (range) treatment duration was 6 (1-18; Arm A), 14 (1-27; B), and 8 (2-26; C) months. Overall response rates (ORRs) were: Arm A, 25% (median time to response [MTTR], 4.3 months); Arm B, 90.9% (MTTR, 1.9); Arm C, 37.5% (MTTR, 4.4). No significant difference was observed between pts with and without CXCR4-mut. At 1,200 mg, 1 DLT (grade 3 clinical TLS), due to pre-existing renal impairment, was reported. At 1,000 mg, 1 grade 3 laboratory TLS occurred in Arm B because of dehydration and active symptomatic therapies; abnormal electrolytes resolved after 1 day of drug interruption, without recurrence. Grade ≥ 3 lisaftoclax-related AEs included neutropenia (13%), leukocytopenia (4.3%), anemia (2.2%), weight loss (2.2%), and septic shock (2.2%). Ventricular arrhythmias were not observed. Only 1 pt required dose reduction (due to neutropenia). MTD has not been reached. A total of 14 pts discontinued study treatment because of disease progression (n = 5) and AE (n = 1). Lisaftoclax plus ibrutinib showed a PK exposure comparable to ibrutinib alone, indicating no potential DDI. Conclusions: Lisaftoclax alone or combined with ibrutinib/rituximab demonstrated measurable effects in pts with naïve or BTKi-treatment-failed WM. Internal study identifier: APG2575WU101. *SA and ML are co-first authors. Clinical trial information: NCT04260217 . [Table: see text]

7543 Background: Total metabolic tumor volume (TMTV) and maximum standardized uptake value (SUVmax) may improve upon standard 18F-fluorodeoxyglucose positron emission tomography/computed tomography (PET-CT)-based assessment of advanced DLBCL during treatment. We report the association of TMTV and SUVmax changes at interim PET-CT (PET2) on survival outcomes in patients with primary refractory DLBCL (prDLBCL) and early relapsing DLBCL (erDLBCL). Methods: Adult patients with prDLBCL (less than a complete response (CR) or progression by the end of treatment (EOT)) or erDLBCL (CR at EOT with relapse within 12 months) between 2005 and 2019 at Mayo Clinic Rochester were included. The % change (Δ) from baseline to PET2 (after 2 cycles of 1L therapy) of TMTV and SUVmax were measured. A PET segmentation threshold of 1.5 liver mean SUV + two standard deviations with a minimum volume constraint of 0.5 mL was utilized (MIM Software, Inc., Cleveland OH, USA) with manual input as needed. Functional splines analysis determined SUVmax and TMTV threshold for analysis. Results: 131 patients had complete PET-CT data (N=79 prDLBCL, N=52 erDLBCL). Baseline median TMTV and SUVmax were 767.4 cm3 (range 0.9-6840.4) and 20.5 (2.0-52.6), respectively. At a median follow up of 77.6 months, 81 patients had died. 2-year OS rate was 53% (95% CI: 42-67) for patients with a PET2 ΔSUVmax decline ≥65% compared to 15% (95% CI: 7-29) for patients with a PET2 ΔSUVmax decline <65%(p<0.001). PrDLBCL had a 2-year OS rate of 48% (95% CI: 31-74) for a ΔSUVmax ≥65% compared to 7% (95% CI: 2-21) for a ΔSUVmax <65%(p<0.001), which captured 58% of prDLBCL patients (N=46). Two-year OS rate was 43% (95% CI: 34-54) for patients with a ΔTMTV ≥75% compared to 5% (95% CI: 1-35) for patients with ΔTMTV <75% (p<0.001). All patients with a ΔTMTV <75% had prDLBCL. PrDLBCL had a 2-year OS rate of 28% (95% CI: 18-44) for a ΔTMTV ≥75%. The outcomes for ΔSUVmax <65% and ΔTMTV <75% at PET2 remained significant in a cox regression model adjusted for IPI and bulky disease (>10cm)(Table). Conclusions: A ΔTMTV decline <75% or a ΔSUVmax decline <65% at PET2 identified an ultra-high-risk subgroup of DLBCL with particularly poor outcomes, that captured a high percentage of prDLBCL patients, and was significant after adjusting for IPI and bulky baseline disease. These patients may benefit from clinical trials evaluating alternative PET-adapted treatment strategies, but further evaluation among all patients with DLBCL is needed. [Table: see text]

7530 Background: Oncolytic virotherapy is a novel immunomodulatory therapeutic approach currently under study for relapsed refractory (R/R) hematologic malignancies. The engineered Vesicular Stomatitis Virus VSV-IFNβ-NIS used in this study encodes interferon beta (IFNβ) and sodium iodine symporter (NIS). Virally-encoded IFNβ serves as an index of viral proliferation and enhances host anti-tumor immunity. Herein, we report the updated results of the phase 1 clinical trial NCT03017820 of a one-time administration of systemic VSV-IFNβ-NIS among patients (pts) with R/R multiple myeloma (MM), T cell Lymphoma (TCL) and Acute myeloid Leukemia (AML) with particular focus on the TCL cohort treated at the highest dose level (DL4) without Ruxolitinib. Methods: VSV-IFNβ-NIS was administered as a single IV dose following a classical 3+3 phase I trial, starting at 5e9 TCID50 DL1 through 1.7e11 TCID50 DL4. A dose expansion cohort of 8 additional R/R TCL pts was added at DL4 in view of an initial signal of activity. The primary objective was to determine the maximum tolerated dose of VSV-IFNβ-NIS as a single agent. Secondary objectives were determination of safety profile and preliminary efficacy of VSV-IFNβ-NIS. Adverse events (AEs) are reported based on CTCAE V4; cytokine release syndrome (CRS) grading was based on Lee (Blood 2014) criteria. Results: To date, a total of 43 pts received VSV-IFNβ-NIS: MM (N=21), TCL (N=21) and AML (N=1). In the TCL cohort: at DL4 Group A (no Ruxolitinib), 12 pts were registered, but only 11 pts were treated (mycosis fungoides (MF) N=3; ALK- ALCL N=1; PTCL-NOS N=2; AITL N=4; Nodal PTCL, TFH N=2; ages 33-79). These pts received a median of 3 lines of therapy (range: 1-5). No dose limiting toxicities were observed. Grades 3 and higher AEs were hematologic with transient lymphopenia (63.6%), neutropenia (36.4%) being the most common. The non-hematologic AEs observed included unique toxicities such as CRS grades 1-2 (81.8%); the transient transaminitis grade 1-2 (36.4%) and grade 3 (27.3%) along with thrombocytopenia grade 1-2 (63.6%) and grade 3 (18.2%) were a reflection IFNβ toxicity. All the AEs observed were short lived. Responses were seen in pts with PTCL. At DL4, in pts with systemic PTCL (N=9), there were 5 responses including 3 complete responses (CR) with two long-lasting at 24 months, an ongoing 15 month CR, and a 5 month CR, and 2 partial responses (PR) lasting 5 months in one pts and 6 months in the other. Conclusions: These updated results of single agent VSV-IFNβ-NIS which include pts with PTCL treated at the highest dose level and a dose expansion cohort demonstrates not only the safety of VSV-IFNβ-NIS but also a strong efficacy signal in pts with PTCL with impressive durable responses. Two expansion cohorts at DL4 have been added (20 additional PTCL, 10 B-cell lymphoma pts) to obtain additional data on tolerability and efficacy and biomarkers of response in these pts. Clinical trial information: NCT03017820 .

7526 Background: The TRANSFORM primary analysis (PA; NCT03575351) confirmed the superior efficacy of liso-cel vs SOC as 2L therapy in patients (pts) with primary refr or early rel LBCL (Abramson et al. Blood 2022). Response to first-line (1L) therapy (refr vs rel), which was a study randomization stratification factor, may influence future treatment response. Here, we present results for refr and rel LBCL subgroups from the TRANSFORM PA. Methods: TRANSFORM is a randomized phase 3 study of liso-cel vs SOC (salvage chemotherapy [CT] followed by high-dose CT [HDCT]/autologous SCT [ASCT]) in adults ≤ 75 y with LBCL primary refr to or rel ≤ 12 mo after 1L therapy and eligible for HDCT/ASCT. The primary endpoint was event-free survival (EFS); key secondary endpoints were CR rate, PFS, and OS. In this predefined subgroup analysis, refr was SD, PD, PR, or CR with rel < 3 mo after 1L therapy; rel was CR with rel ≥ 3 mo and ≤ 12 mo after 1L therapy. Results: 92 pts were randomized to each arm. Most pts in the liso-cel and SOC arms had refr disease (73% and 76%, respectively; rel disease, 27% and 24%). Baseline characteristics in the refr and rel subgroups, respectively, were generally balanced: median LDH (U/L; liso-cel, 228.5 and 225; SOC, 259 and 259); median SPD (cm2; liso-cel, 11 and 12; SOC, 15.5 and 18); high-grade B-cell lymphoma (liso-cel, 27% and 16%; SOC, 27% and 9%); diffuse LBCL not otherwise specified (liso-cel, 58% and 56%; SOC, 49% and 73%). Consistent with the overall study population, EFS, CR rate, and PFS favored liso-cel vs SOC in both subgroups (Table). Safety was also consistent. Grade ≥ 3 cytokine release syndrome (CRS) and neurological events (NE) were low in refr (1% and 4%) and rel (0 and 4%) subgroups, respectively, with no grade 4/5 CRS or NEs. Conclusions: In TRANSFORM, liso-cel showed benefits in EFS, PFS, and CR rate vs SOC irrespective of prior response to 1L therapy. As refr LBCL is historically difficult to treat, outcomes for liso-cel in this subgroup are encouraging. Clinical trial information: NCT03575351 . [Table: see text]

7520 Background: With goal of simplifying clinical trials in lymphomas, we reported that bone marrow biopsies are irrelevant for response assessment in most patients (pts) with follicular lymphoma (FL) on trials (Rutherford JCO 2023). We then investigated impact of imaging frequency in FL clinical trials. We hypothesized that progression free survival (PFS) would not be different when imaging is performed less frequently than required by trials. Methods: We identified all trials through Alliance for Clinical Trials in Oncology that enrolled untreated pts with FL from 2008-2016. We considered 2 imaging schedules: protocol specified (control) vs relaxed (X) in which response assessments at every other required time point were omitted. For each trial, we estimated PFS using Kaplan Meier methods for the 2 schedules then determined difference in PFS between schedules as % change from control schedule in 2 year (yr) PFS rate. We performed simulation studies to approximate impact of less frequent imaging on PFS estimation using 50901 (low-intermediate risk FL) and 50904 (intermediate-high risk FL, control arm). We assumed exponential distribution for PFS, where rate parameter was calculated based on observed median PFS with uniform censoring distribution. Protocols for 50901 and 50904 mandated imaging every 4 months (mos) for 2 yrs then every 6 mos (S0). We ran 1000 iterations of 100 observations using 3 tumor assessment follow up schedules: every 6 mos for 2 yrs then yearly (S1), every 8 mos for 2 yrs then yearly (S2), or yearly (S3) for simulated progression times. We calculated deviation of PFS using simulated schedules from truth (S0). Results: Across 5 FL trials, median percent change of schedule X from control schedule in estimated 2yr PFS was 2.1% (0.0-30.8%) and in estimated 4yr PFS was 0.9% (-8.6-25.7%). Disparate result in 50901 is due to small shift in events with low number of pts at risk for progression. Simulation study results by trial were: for 50901, true median PFS 1.9 yrs and average median PFS for S1, S2, and S3 of 2.05, 2.11, and 2.21 yrs; for 50904 (control arm), true median PFS 4.1 yrs and average median PFS for S1, S2, and S3 of 4.16, 4.12, and 4.05 yrs. Conclusions: Our findings support decreased frequency of imaging studies in FL clinical trials, which would improve resource use and decrease pt burden. We plan a larger analysis to confirm results. https://acknowledgments.alliancefound.org . Clinical trial information: NCT00553501 , NCT01145495 , NCT01190449 , NCT01286272 , NCT01829568 .[Table: see text]