Seymour, Erlene Kuizon

7062 Background: MCL is a rare and aggressive subtype of B-cell non-Hodgkin lymphoma that remains incurable. Bruton tyrosine kinase (BTK) inhibitors are an established standard of care for R/R MCL. However, comparative effectiveness data for different BTK inhibitors for R/R MCL are limited. This study evaluated the real-world effectiveness of zanu and acala in US patients with R/R MCL based on overall survival (OS) and time to next treatment (TTNT). Methods: A retrospective cohort study was conducted using Komodo health administrative claims data. Eligible patients were adults (aged ≥18 years) with ≥2 MCL diagnoses and continuous enrollment or activities within 1 year prior to and 3 months following the index date. Patients were required to initiate monotherapy with zanu (index period: November 2019 to August 2025) or acala (index period: October 2017 to August 2025) as a second-line or later (2L+) treatment, with index date defined as the first observed claim for zanu or acala. Patients with evidence of clinical trial participation, end stage renal disease or prior stem cell transplant were excluded. Outcomes included OS (time from index date to all-cause mortality) and TTNT (time from index date to subsequent therapy with an allowable gap of 120 days). If an outcome was not observed, patients were censored at the date of last activity or enrollment end date. Survival analyses were conducted using Kaplan-Meier estimates and Cox proportional hazards models. Inverse probability of treatment weighting (IPTW) was adjusted for age, sex, US region, treatment initiation year and Charlson Comorbidity Index (CCI). Results: In total, 2219 patients (zanu, n=931; acala, n=1288) were eligible and included in the study. The mean age was higher in the zanu (72.3 years; SD, 9.4) vs acala cohort (71.4 years; SD, 9.7). Most patients were male (zanu, 71%; acala, 75%), non-Hispanic white (zanu, 73%; acala, 74%), and the mean CCI was 3.5 (SD, 3.2) and 3.6 (SD, 3.1) in the zanu and acala cohorts, respectively. Median follow-up was 14.8 and 18.2 months in zanu and acala cohorts, respectively. Median TTNT was 26.7 months for zanu and 20.8 months for acala. Median OS was not reached for zanu and was 60.6 months for acala. In the unadjusted model, zanu had a longer TTNT (HR, 0.86; 95% CI, 0.76-0.97; P =.012) and OS (HR, 0.74; 95% CI, 0.62-0.88; P <.001). After IPTW adjustment, TTNT and OS favored zanu treatment (TTNT: IPTW-adjusted HR, 0.86; 95% CI, 0.76-0.98; P =.025; OS: IPTW-adjusted HR, 0.81; 95% CI, 0.68-0.98; P =.03). Conclusions: In this real-world analysis of US health claims data, zanu monotherapy demonstrated significantly longer TTNT and improved OS compared with acala in patients receiving 2L+ therapy for MCL. These findings support zanu as an effective BTK inhibitor for R/R MCL.

Abstract Background The treatment (tx) landscape for chronic lymphocytic leukemia (CLL) has evolved, with National Comprehensive Cancer Network (NCCN) guideline-preferred novel therapies (NTs), such as acalabrutinib, zanubrutinib, and venetoclax-based regimens, now preferred over ibrutinib and chemoimmunotherapy (CIT) in front-line (1L) settings. We previously showed that patients (pts) from different racial/ethnic groups may not have equitable access to NTs. Here, we examined racial/ethnic inequities in 1L NT utilization among US pts with CLL and potential social determinants of health (SDOH) drivers of these inequities. Methods This retrospective cohort study utilized the US-based, electronic health record-derived de-identified Flatiron Health Research Database, linked to neighborhood (US Census track or block group) data from American Community Survey and Agency for Healthcare Research and Quality datasets. Eligible pts included adults with CLL who started 1L tx 01/01/2019-07/31/2024. The primary outcome was receipt of 1L therapy (CIT vs preferred NTs, ibrutinib vs preferred NTs), with NCCN guideline-preferred NTs (v2.2023-v3.2025) as a reference. Associations between race/ethnicity (White, Black, Hispanic) and 1L tx types were assessed using logistic regressions, adjusting for age, sex, year of 1L start, immunoglobulin heavy chain variable region status, and del17p/TP53 status. To better understand which SDOH factors contribute to racial and ethnic inequities in tx utilization, we performed mediation analysis using Multiple Mediation Analysis implemented through nonlinear multiple additive regression tree models. Individual-level (Eastern Cooperative Oncology Group status, practice type, insurance) and 20 area-level SDOH factors measuring social deprivation (defined as limited access to economic, social, neighborhood, physical, or healthcare resources) were assessed as potential mediators. Results Of the 4452 pts included in the study, 3717 were White (83%), 371 were Black (8%), 209 were Hispanic (5%), and 155 were Other race (4%). Black and Hispanic pts were more likely to live in neighborhoods with higher social deprivation, such as residential segregation (predominant race/ethnicity in the area: White, Black, Hispanic, Diverse), with no internet access, no vehicle ownership, and no health insurance coverage. Overall, 37% of pts received a preferred NT, highest among White (38%) pts, followed by Black (35%) and Hispanic (26%) pts. Compared with White pts, Hispanic pts were more likely to receive CIT than preferred NTs (adjusted odds ratio [aOR] 2.12; 95% confidence interval [CI] 1.46-3.09); Black (aOR 1.44; 95% CI 1.05-1.97) and Hispanic pts (aOR 1.83; 95% CI 1.17-2.85) were more likely to receive ibrutinib than preferred NTs. Pts living in areas with the highest social deprivation were less likely than their counterparts in lowest social deprivation neighborhoods to receive preferred NTs. Specifically, residence in predominantly Black or Hispanic neighborhoods (26% or 27% vs 39% predominantly White), areas with lowest socioeconomic status (32% vs 40%), and neighborhoods with the lowest levels of internet access (32% vs 39%), vehicle ownership (32% vs 39%), and health insurance coverage (34% vs 41%) was associated with lowest receipt of preferred NTs. In the mediation analysis, individual- and area-level SDOH factors explained 94.4% (95% CI 2.9-185.9) of the observed Black-White inequity in receipt of ibrutinib versus preferred NTs; residential segregation appeared to be the most important mediator (59.7%; 95% CI −3.5 to 123.0). Similarly, the Hispanic-White inequity in receipt of preferred NTs was driven by the combined effect of area-level SDOH and individual-level variables (88.5%; 95% CI 45.6-131.3), with residential segregation as the main driver (48.3%; 95% CI 10.7-85.9), followed by practice setting (9.8%; 95% CI −3.5 to 23.1). In contrast, measured SDOH factors did not explain the inequity in receipt of CIT versus preferred NTs between Hispanic and White pts (21.5%; 95% CI −8.3 to 51.4), suggesting that other factors may contribute to the observed inequities. Conclusion Black and Hispanic pts with CLL were less likely than White pts to receive preferred NTs. A significant proportion of these disparities was explained by area-level SDOH, particularly residential segregation. These findings underscore the need to address structural barriers to ensure equitable access to emerging, guideline-recommended treatments.

Abstract Background Chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) is the most common leukemia in US adults and incidence increases with age. Although the treatment (tx) landscape has evolved, it is unclear whether tx selection differs for older patients (pts), given concerns around comorbidities, toxicity, and efficacy. There is a need to better understand pt characteristics, tx patterns, and biomarker use among pts aged ≥65 yrs with CLL/SLL in the current therapeutic era. Methods A retrospective longitudinal study was conducted using the de-identified 100% Medicare Fee-for-Service (FFS) Research Identifiable Files. Included pts were diagnosed with CLL/SLL at age ≥65 and initiated first-line (1L) tx 1/1/2020-9/30/2024 (with ≥12 mo in database prior to 1L tx start). Index date was defined as date of 1L tx start, and pts were followed to death, end of Medicare enrollment, or study end, whichever occurred first. 1L tx was defined as any CLL pharmacologic tx within the first 90 days of index date. Tx utilization was summarized as the number and proportion of pts who received each tx at each line. Descriptive statistics were used to summarize demographic and social characteristics and baseline comorbidities, in all pts and by 1L tx. Proportion and timing of documented biomarker orders any time prior to index were summarized by test type (CLL fluorescence in situ hybridization [FISH], TP53 DNA sequencing and immunoglobulin heavy chain variable region [IGHV] test) and by 1L tx. Results Of the 21,008 pts included, median age was 76.4 yrs at 1L tx, with 43% of pts aged 65-74 yrs, 43% aged 75-84 and 14% aged ≥85. The majority of pts were male (58%) and White (91%). About 8% and 9% of pts had dual eligibility status and low-income subsidy, respectively. Median Charlson Comorbidity Index (CCI) was 4 (range: 1-21), with 40% of pts having CCI ≥5. Covalent Bruton tyrosine kinase inhibitor (cBTKi) monotherapies (mono) were most common at 1L tx (41%), including 10% zanubrutinib (zanu), 15% ibrutinib (ibr), and 16% acalabrutinib (acala). B-cell lymphoma 2 (BCL2)+anti-CD20 monoclonal antibody (mAb) was less common (11%), and chemoimmunotherapy (CIT) was used by 13% of pts, mostly BR (8%) and FCR (3%). Other less common tx included cBTKi+anti-CD20mAb (6%) or cBTKi+BCL2 therapies (1%). Among remaining pts, most received anti-CD20mAb (22%). The use of cBTKi mono increased from 41.7% in 2020 (ibr 30.6%; acala 11.1%) to 47.6% in 2024, driven by increased use of zanu (27.8%; acala 15.7%; ibr 4.2%). BCL2+anti-CD20mAb increased from 9.2% in 2020 to 12.6% in 2024. Pts treated with cBTKi mono were older than those with BCL2+anti-CD20mAb (median age 77.2 vs 74.5), and more likely to have dual eligibility status (10% vs 4%) or low-income subsidy (11% vs 5%). More pts who received zanu mono had CCI ≥5 (39%) versus acala (36%), ibr (35%), or BCL2+anti-CD20mAb (32%). Pts with BCL2+anti-CD20mAb were less likely to have diabetes (23% vs 26%), congestive heart failure (CHF; 16% vs 19%), chronic pulmonary disease (23% vs 27%), and renal diseases (23% vs 27%). Pts with ibr were less likely to have myocardial infarction (29% vs 34%), coronary artery disease (22% vs 25%), CHF (16% vs 19%), and atrial fibrillation (12% vs 18%). Overall, 69% of pts had FISH testing prior to 1L tx, but test orders for TP53 (12%) or IGHV (28%) status were infrequent. Pts with ibr had the lowest rates of TP53 tests (6%), whereas pts with CIT had the lowest rates of IGHV tests (16%). The timing of tests showed a binomial distribution where most pts received FISH, TP53, or IGHV tests either ≤60 days prior to 1L tx (46%, 50%, 33%), or &gt;1 yr before 1L tx (30%, 22%, 43%). Among pts who received ≥2 lines of therapy for CLL (n=4428; 21%), cBTKi mono was the most common in 2L (41%), including 14% zanu, 17% acala, and 10% ibr. CIT and BCL2+anti-CD20mAb were used in 12% and 9% of pts, respectively. Only 634 (3%) pts had 3L+ tx, of whom 33% received cBTKi mono, including 16% zanu, 12% acala, and 5% ibr (5%). Conclusion This large real-world study found that cBTKi mono was the most common 1L tx choice among pts aged ≥65 with CLL/SLL, with increased use of next-generation cBTKi. Pts with more baseline comorbidities were less likely to receive ibr or BCL2-based tx. FISH testing was not performed in nearly one-third of pts, and most pts did not have TP53 or IGVH sequencing prior to tx. Future studies are needed to continue to evaluate evolving tx paradigms in older pts with CLL/SLL.

Abstract This real-world retrospective cohort study evaluated utilization and comparative effectiveness of covalent Bruton tyrosine kinase inhibitor (cBTKi) monotherapies in relapsed/refractory mantle cell lymphoma (R/R MCL) from electronic health records in the United States. Adults with R/R MCL who received second- or third-line (2L/3L) zanubrutinib, acalabrutinib, or ibrutinib monotherapy, on or after 1 January 2018, were included. Inverse probability of treatment weighting was used in adjusted Cox models to compare real-world time-to-next treatment (rwTTNT) and overall survival (rwOS). Among 698 patients who received 2L/3L cBTKi monotherapy, 49%, 32%, and 19% received acalabrutinib, ibrutinib, and zanubrutinib, respectively. Unadjusted analyses showed median rwTTNT for 2L zanubrutinib, acalabrutinib, and ibrutinib was 14.5 (95% confidence interval [CI], 11.0-23.2), 12.8 (95% CI, 10.5-15.6), and 10.3 (95% CI, 7.6-13.7) months, and median rwOS was 26.4 (95% CI, 23.2 to not reached [NR]), 29.2 (95% CI, 22.9-38.1), and 29.3 (95% CI, 21.8-41.6) months, respectively. Median rwTTNT for 3L zanubrutinib, acalabrutinib, and ibrutinib was 21.1 (95% CI, 3.9 to NR), 9.2 (95% CI, 6.8-14.7), and 9.6 (95% CI, 4.8-18.0) months, and median rwOS was NR (95% CI, 27.3 to NR), 27.4 (95% CI, 15.1-42.2), and 27.0 (95% CI, 15.6 to NR) months, respectively. Adjusted models in the 2L/3L cohorts combined showed numerically longer rwTTNT and statistically significantly longer rwOS for zanubrutinib vs ibrutinib (hazard ratio, 0.63; 95% CI, 0.42-0.96), and trends for improved rwTTNT and rwOS for zanubrutinib over acalabrutinib. Toxicity was a frequent reason for changing to another cBTKi. These findings suggest potential improvements in rwTTNT and rwOS with the use of second- and next-generation cBTKis for R/R MCL from 2018 and beyond.

e13741 Background: The NCCN guidelines for first-line (1L) regimens in CLL have evolved over the past decade, shifting from ibrutinib (ibr) and chemoimmunotherapy (CIT) to second-generation BTK inhibitor and venetoclax combinations. We evaluated real-world use of preferred 1L treatment (tx) since 2016 in CLL patients (pts) in routine care to identify differences in prescribing based on race/ethnicity and practice type. Methods: This retrospective observational study utilized the US nationwide Flatiron Health electronic health record-derived de-identified database. Eligible pts had confirmed CLL and initiated 1L tx between 01/01/16-07/31/24. Primary outcome was receipt of preferred 1L tx defined by NCCN guidelines in four time periods by race/ethnicity (Hispanic, White, Black, Asian/Other). Odds ratios (ORs) were estimated using logistic regression, additionally adjusting for age, sex, ECOG performance status, IGHV, del17p/ TP53 mutation status, time period, and practice type. Results: A total of 7528 pts were included. Compared with White pts (n = 5472), Black pts (n = 640) were younger (median age at 1L: 68 vs 71). More Black and Hispanic (n = 290) pts were treated at community practices (86% vs 80% White). Of those pts tested, more Black pts had unmutated IGHV than White (77% vs 56%). Presence of del17p/ TP53 mutation was similar across races/ethnicities. The proportion of pts receiving preferred 1L tx based on the NCCN Guidelines significantly differed by race/ethnicity (Table) ( P = 0.0021). The proportion of Hispanic pts treated with preferred 1L tx was significantly lower than White (OR = 0.61; 95% CI: 0.47-0.79), but Black was similar to White (OR = 1.07; 95% CI: 0.89-1.30). Updates to NCCN guidelines were significantly associated with pts receiving preferred 1L tx by practice type ( P = 0.0005). In 2016-2018, 44% of community practices and 55% of academic centers adopted targeted therapies (TTs); in 2019, ibr use increased in both practices (77% vs 68%, respectively). Adherence to preferred tx improved across practices in 2020 but decreased with the prioritization of second-generation therapies. After the approval of zanu, use of TTs was 71% in community practices and 74% in academic centers. Conclusions: Inequities in pts with CLL receiving preferred 1L tx suggests disproportionate use of CIT and ibr by race/ethnicity. Use of preferred TTs also differed by practice type and time period, with increased adoption after pivotal trials. Time period % Pts receiving preferred tx by race a White Black Hispanic Asian/Other 2016-2018:Preferred tx ibr 46% 50% 43% 45% 2019(v2.2019: Jan 2019)Preferred tx ibr 76% 76% 67% 79% 2020-Jun 2022(v4.2020: Feb 2020)Preferred tx acala, VO, ibr 84% 84% 69% 83% Jul 2022-Jul 2024(v2.2023: Aug 2022)Preferred tx acala, VO, zanu 72% 66% 56% 73% VO, venetoclax + obinutuzumab. a By listing of NCCN preference (preferred vs other) among non-del17p and age >65.

Introduction: Treatments for R/R MCL have evolved with NTs, including BTK inhibitors (BTKis). Little is known about RW treatment patterns and clinical outcomes of pts with R/R MCL for chemoimmunotherapy (CIT) vs NTs among pts of different race/ethnicity. Data on RW testing and clinical outcomes of pts with R/R MCL harboring a TP53 mutation are limited. Methods: This retrospective cohort study included adult pts with R/R MCL who initiated second-line (2L) or third-line (3L) treatment on 1/1/2018 or later and were followed up until loss to follow-up, death, or data cut-off using US Flatiron Health electronic health record-derived de-identified databases. Median RW time to next treatment (mrwTTNT) and median RW overall survival (mrwOS) were estimated based on Kaplan-Meier analyses and adjusted for age and sex. CIT included any MCL treatment with chemotherapy + anti-CD20 antibody. NTs included BTKis, BCL2 inhibitors, lenalidomide, bortezomib, and CAR-T, or combinations. Results:This study included 1,377 pts with R/R MCL who received 2L+ therapy. Of these, 1,028 (75%) were non-Latinx (NL)-White, 53 (4%) were NL-Black, 86 (6%) were Latinx, 108 (8%) were NL-Asian or other race, and 102 (7%) were of unknown/undocumented race. The overall 2L+ population had a median age of 71 y (range 63-78), were mostly male (74%), had a diagnosis of MCL not otherwise specified (NOS; 85%), and had stage IV disease (62%). Sixty-three percent had disease progression within 24 mo from first-line (1L) treatment (POD24) before starting 2L therapy. Relative to all pts, NL-Black and NL-Asian/other race pts had more variants of MCL (blastic, leukemic, pleomorphic) and higher Ki67% and lactose dehydrogenase (LDH) levels at 2L/3L index date. In contrast, Latinx pts had more MCL NOS (92%) and lower Ki67% and LDH levels at 2L index date. More NL-Black and unknown race pts had POD24 than did other races (70% and 76%, respectively). Overall, the most common NTs used were BTKis. 1L treatments were bendamustine-rituximab (BR; 54%), R-CHOP (18%), and cytarabine-containing CIT (9.7%). The most common 2L treatments were BR (32%), acalabrutinib (31%), ibrutinib (21%), zanubrutinib (11%), and RCHOP (11%). The most common 3L therapies were BR (34%), acalabrutinib (21%), zanubrutinib (12%), ibrutinib (10%), R-CHOP (9.2%), and brexucabtagene autoleucel (7.4%). Transplantation rates before 2L and CAR-T use in 3L was highest among White pts. When assessing mrwTTNT and mrwOS by therapy in 2L, 766 pts (70%) received NTs and 333 (30%) received CIT. Among all pts, mrwTTNT (mo [95% CI]) was longer with 2L NT (11.9 [10.6, 14.5]) vs CIT (9.9 [8.1, 12.9]). NL-White, NL-Black, and NL-Asian/other race pts had longer mrwTTNT with NT (11.9 [10.5, 14.6], 12.9 [7.6, NR], and 14.6 [8.5, 21.4], respectively) vs CIT (9.9 [7.6, 12.9], 9.7 [3.0, NR], and 6.0 [3.2, 21.2]). Latinx pts had longer mrwTTNT with CIT (14.9 [11.8, NR]) vs NT (9.0 [3.8, 24.2]). Among all pts, mrwOS (mo [95% CI]) was longer with 2L CIT (43.0 [34.1, 56.5]) vs NT (35.6 [29.9, 41.2]). White and Latinx pts had longer mrwOS with CIT (47.3 [33.9, NR] and NR [33.3, NR], respectively) vs NT (35.0 [28.8, 48.4] and 42.3 [31.0, NR]). Black and Asian/other race pts had longer mrwOS with NT (41.2 [32.8, NR] and 38.8 [23.5, NR], respectively) vs CIT (34.8 [9.7, NR] and 13.5 [8.3, NR]). Among all 3L pts (n=364 on NTs, n=119 on CIT), mrwTTNT (mo [95% CI]) improved when using NTs (7.9 [6.8, 10.3]) vs CIT (4.4 [3.5, 6.9]). NTs demonstrated better mrwTTNT vs CIT in all race/ethnic groups except Latinx pts. For all race/ethnic groups, mrwOS was improved with NTs (32.5 [24.7, 42.6]) vs CIT (19.5 [13.7, 47.3]). Overall RW testing for TP53 aberrations was limited, with 72 pts (5%) found to be positive for a TP53 mutation. For pts with TP53 mutations, mrwTTNT and mrwOS were longer for 2L NTs (3.3 [2.2, 6.4] and 18.3 [9.0, NR], respectively; n=42) vs CIT (3.0 [1.9, 7.6] and 15.0 [7.2, NR]; n=16). Conclusions: High-risk features, treatment patterns, and clinical outcomes for NTs vs CIT in R/R MCL differed by race/ethnicity. Use of 2L+ NTs was associated with a trend towards improved mrwTTNT and mrwOS among NL-Black and NL-Asian/other race pts. NT use in 3L numerically improved mrwTTNT and mrwOS for most pts vs CIT. RW pts with TP53 mutations had a poor prognosis and numerically improved outcomes with the use of 2L NT, although testing remains limited. Future research evaluating reasons for these differences and increased RW TP53 testing is warranted.

Introduction: Treatment for R/R MCL has evolved with the use of cBTKi monotherapy. Previously, we reported differences in RW time to next treatment (rwTTNT) and overall survival (rwOS) among patients (pts) treated with ibrutinib (ibr), acalabrutinib (acala), and zanubrutinib (zanu), but reasons for the differences were unknown (Phillips et al. EHA 2024). Our objectives were to re-evaluate trends in rwTTNT and rwOS; assess treatment patterns of cBTKis, including switching; describe reasons for cBTKi discontinuation; and compare RW effectiveness of ibr, acala, and zanu monotherapy. Methods: This retrospective cohort study included adult pts diagnosed with R/R MCL who initiated second-line (2L) or third-line (3L) first cBTKi treatment 01/2018-11/2023 and were followed until loss to follow-up or death using the US nationwide Flatiron Health EHR deidentified database. Patient characteristics and survival estimates based on Kaplan-Meier (KM) analyses were summarized. Adjusted analysis using a multivariate Cox model was applied to assess rwTTNT and rwOS. Key model variables were age, sex, POD24 (2L start ≤24 mo from first-line start), and number of prior lines of therapy. Reasons for discontinuation were abstracted from documentation in notes and included non-mutually exclusive categories. Results: This study included 698 pts who received cBTKi monotherapy in 2L or 3L for MCL. The median age at cBTKi start was 73 (range, 34-85 yrs); the majority of pts were male (74%) and White (White 78%, Black 3.2%, Asian 1.3%, Other Race 7.6%, Unknown 10%) and non-Hispanic/Latino (non-Hispanic/Latino 74%, Hispanic/Latino 6.0%, Unknown 20%). Patients varied by socioeconomic status (Yost index 1 [12%], 2 [16%], 3 [19%], 4 [24%], 5 [19%], Unknown [10%]). Patients also varied by baseline ECOG performance status, Ki67, comorbidities, and LDH. Most pts had stage III/IV at diagnosis (75%). Among pts who received a cBTKi at 2L or 3L index therapy, 135 received zanu (2L [79%], 3L [21%]), 342 received acala (2L [76%], 3L [24%]), and 221 received ibr (2L [75%], 3L [25%]). Follow-up time (median [IQR]) from start of 2L/3L for each cBTKi were zanu 15 mo (10, 25), acala 36 mo (20, 52), and ibr 57 mo (35, 67). Among the overall 2L/3L cBTKi monotherapy cohort, median rwTTNT was 11.5 mo (95% CI 10.0, 13.5) and median rwOS was 30.4 mo (24.7, 36.1). For each cBTKi therapy in unadjusted KM analyses, median rwTTNT for zanu was 16.8 mo (95% CI 11.1, 23.2), acala 11.9 mo (9.2, 14.6), and ibr 9.8 mo (7.6, 13.1); median rwOS was 28.8 for zanu (95% CI 23.7, not reached), acala 29.2 mo (22.9, 36.5), and ibr 29.3 mo (21.2, 39.1). Adjusted multivariate model showed a trend of longer rwTTNT with zanu compared to ibr (HR 0.76 [95% CI 0.57, 1.01]; P=.06) and acala (0.88 [0.67, 1.16]; P=.40), and significantly longer rwOS for zanu compared to ibr (0.67 [0.46, 0.98]; P=.04) but a nonsignificant trend in rwOS favoring zanu compared to acala (0.73 [0.51, 1.05]; P=.09). Forty-seven pts (6.7%) who received cBTKi monotherapy in 2L or 3L switched to another cBTKi; 31 (4.4%) switched from ibr to acala or zanu, 12 (1.7%) from acala to zanu, and &lt;5 (0.1%) from zanu to acala. Reasons for discontinuation (~60% documented in cohort) varied by cBTKi monotherapy use. The most common documented reasons for discontinuation were disease progression (30% overall; zanu [24%], acala [35%], ibr [26%]) and toxicity (11% overall; zanu [7%], acala [10%], ibr [17%]). Among pts who switched from one cBTKi to another, the most documented reason for discontinuation was toxicity for ibr to acala or zanu (61%) and for acala to zanu (58%). Other reasons included financial (1%), non-cancer-related medical issue (4%), cancer-related symptoms not due to therapy (2%), and pt request (1%). Conclusions: Among RW pts with R/R MCL who received cBTKi monotherapy, zanu had a longer rwOS compared to ibr, and a trend of longer rwTTNT and rwOS compared to acala. Reasons for discontinuation were most commonly disease progression and toxicity. Among pts who switched cBTKis, the most common reason for switching was toxicity, which provides a broader scope of reasons for differences in rwTTNT that are not exclusive to disease progression.