Chemoimmunotherapy Research Articles

CLL-033 Is COVID-19 Infection a Trigger for Progression of CLL?

Introduction: COVID-19 diagnosed in chronic lymphocytic leukemia (CLL) could have a severe evolution with many complications. Chemo immunotherapy and immunological status could be the main causes of this evolution. The aim of this study was to check if COVID-19 could associate with a progression of CLL. Materials and Methods: The retrospective study included 40 CLL patients (33 male and 7 female) with a median age of 64.5 (95% CI for median: 59-67) who were admitted to the Hematology Department Colentina between March 2020- March 2022). These patients were diagnosed with COVID-19 by PCR test and were evaluated from 2020 to 2022. Results High count of leucocytes (WBC)- more than 50 × 1000/µL was identified in 15 patients (37.5%). Persistence of hyperleukocytosis after 1 month of evolution was identified in 10 patients, in 7 of them starting treatment was needed, all these patients were in the watch and wait for the group before the onset of COVID-19. Infection of SARS-Cov-2 diagnosed in CLL patients was associated with refractory status and progression of CLL during the follow-up period, a switch to another line of treatment was needed. Long COVID is defined as persistence long time for symptoms and the positivity of the PCR test was directly correlated with an immune deficit (r=0.37, p=0.01). Thrombotic complication developed by CLL patients during COVID-19 evolution was associated with vascular risk presence (diabetes mellitus, arterial hypertension, thrombosis history- stroke or myocardial infarction) –(r=0.61, p=0.0001). Unfavorable evolution was highly correlated with high severity of pneumonia/respiratory insufficiency and immune deficiency presence; the high count of WBC at the onset or during the first month of COVID-19 was not associated with a high risk of deceased. Conclusion COVID-19 could be a trigger for the progression of CLL. A strong analysis of the high cohort is needed. The immune deficit is involved in the severity of COVID-19 and the unfavorable evolution of the patients. Vascular risk presence in CLL patients is associated with thrombotic complication.

OA12.04 Efficacy of Nivolumab and Temozolomide in Extensive Stage Small Cell Lung Cancer after Chemo-Immunotherapy: A Phase 2 Trial.

Treatment options are limited in patients with extensive stage small cell lung cancer (ES-SCLC) after progression on first line chemo-immunotherapy (CIT). Temozolomide (TEM) is active in ES-SCLC and has been shown to have immunomodulatory impact in patients with advanced cancers, however data are unavailable in patients after CIT. We present the final analysis of a phase 2 trial of combination nivolumab and TEM in patients with ES-SCLC as 2nd or 3rd line after progression on CIT.

Clinical and economic burden of tumor lysis syndrome among patients with chronic lymphocytic leukemia/small lymphocytic lymphoma: A real-world US retrospective study.

BACKGROUND: Tumor lysis syndrome (TLS) is a potentially fatal complication of antineoplastic treatments for hematologic malignancies, including chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma (SLL). Patients developing TLS require intensive care, adding to the overall clinical and economic burden of CLL/SLL. OBJECTIVE: To analyze TLS-associated health care resource utilization (HCRU) and costs in patients with CLL/SLL treated with regimens associated with a high TLS risk (per treatment guidelines), ie, anti-CD20-based chemoimmunotherapy (CIT), lenalidomide, obinutuzumab, or venetoclax. METHODS: Adult patients with CLL/SLL in the MarketScan Databases (January 1, 2006, to April 30, 2020) initiated on CIT, lenalidomide, obinutuzumab, or venetoclax (index date) on or after January 1, 2007, were included in the analysis. Treatment-emergent TLS was defined as TLS occurring in the first 90 days of active treatment. The post-index period was divided into 30-day intervals until the end of the index regimen; intervals pre-TLS were non-TLS intervals and those starting from the TLS event were TLS intervals. Per-patient-per-month (PPPM) HCRU and costs were compared between TLS and non-TLS intervals using generalized linear models adjusted for baseline and time-varying confounders. The proportion of patients in the TLS cohort (patients with treatment-emergent TLS) and non-TLS cohort (patients with no treatment-emergent TLS) who switched treatment within 90 days post-index was compared using Kaplan-Meier rates with logrank P values. RESULTS: Among 6,343 patients with CLL/SLL, 71 (1.1%) developed treatment-emergent TLS (venetoclax: 11.5%; other regimens: 0.8%) after a mean (median) of 12.7 (7.0) days following treatment initiation (mean [median] duration of index regimen: 16.0 [10.0] months); 12 (0.2%) developed clinical TLS (venetoclax: 3.1%; other regimens: 0.1%). TLS was associated with 1.7 times more inpatient admissions (P < 0.001), 2 times more days of inpatient stay (P = 0.012), 22% fewer days of antineoplastic drug administration (P = 0.020), and $3,062 PPPM higher health care costs (P = 0.016), which were mainly driven by $1,688 PPPM higher inpatient costs (P = 0.044). Higher costs were observed among both patients who initiated venetoclax (TLS: $24,170; non-TLS: $20,091) and those who initiated other regimens (TLS: $8,746; non-TLS: $6,915). More patients in the TLS vs non-TLS cohort switched treatment in the first 90 days of treatment (12.6% vs 5.1%, P = 0.006). CONCLUSIONS: TLS was associated with a substantial cost burden (driven by inpatient costs) and higher rate of treatment switching (vs non-TLS cohort) in patients with CLL/SLL treated with CIT, obinutuzumab, lenalidomide, or venetoclax. The risk of treatment-emergent TLS and associated incremental HCRU and costs, as well as the potential impact on quality of life, should be weighed when evaluating the risk-benefit of therapies in CLL/SLL management. DISCLOSURES: Dr Rogers has received research funding from Genentech, AbbVie, Novartis, and Janssen (not for the present study); consulting fees from Acerta Pharma, AstraZeneca, Innate Pharma, Pharmacyclics, Genentech, and AbbVie; and travel funding from AstraZeneca. Mr Emond, Mr Kinkead, Ms Lafeuille, and Mr Lefebvre are employees of Analysis Group, Inc., which has provided paid consulting services to Janssen Scientific Affairs, LLC. Drs Lu and Huang are employees of Janssen Scientific Affairs, LLC, and stockholders of Johnson & Johnson. Ms Côté-Sergent was an employee of Analysis Group, Inc., at the time the study was conducted. This study was funded by Janssen Scientific Affairs, LLC. The sponsor was involved in the study design; data collection, analysis, and interpretation; manuscript writing; and the decision to publish the article.

EP14.05-004 Temozolomide and Atezolizumab as Second Line Treatment for Extensive Stage Small Cell Lung Cancer: A Randomized, Multi-Cohort Phase 2 Trial

Treatment options are limited for patients with extensive stage small cell lung cancer (ES-SCLC) after progression on first line chemo-immunotherapy (CIT). Temozolomide (TEM) is active in ES-SCLC and has been shown to have an immunomodulatory effect for patients with advanced cancers. Immune checkpoint inhibitor (ICI) therapy combined with TEM has demonstrated promising activity among patients in 2nd and 3rd line after CIT (NCT03728361, reported at this meeting). Two different dosing regimens of TEM monotherapy have been explored in ES-SCLC but the objective response rate among patients treated after first line CIT remains unknown.

1051P Radiotherapy (RT) and efficacy of immune checkpoint inhibitors (ICI), chemotherapy (CTx) and chemoimmunotherapy (CIT) in patients with non-small cell lung cancer (NSCLC)

Preclinical and retrospective clinical studies have suggested that local RT enhances the activity of ICI mediated by the so called abscopal effect – a systemic response in metastatic cancer induced by local irradiation. The most recent prospective trials have not been able to support this hypothesis.

The Promising Role of Natural Exosomal Nanoparticles in Cancer Chemoimmunotherapy.

Exosomal nanoparticles are cell-derived nano-sized vesicles in the size range of 30-150nm formed by the inward infolding of the cell membrane. They are encased in a lipid bilayer membrane and contain various proteins and nucleic acids according to the characteristics of their parent cell. They are involved in intercellular communication. Their specific structural and inherent properties are helpful in therapeutics and as biomarkers in diagnostics. Since they are biomimetic, these small-sized nanoparticles pose many advantages if used as a drug carrier vehicle. In cancer, the exosomal nanoparticles have both stimulatory and inhibitory activity towards immune responses; hence, they are used in immunotherapy. They can also carry chemotherapeutic agents to the target site minimizing their targetability concerns. Chemoimmunotherapy (CIT) is a synergistic approach in which chemotherapy and immunotherapy are utilized to benefit each other. Exosomal nanoparticles (NPs) are essential in delivering CIT agents into tumor tissues. Most advanced studies in CIT take place in the stimulator of interferon genes (STING) signaling pathway, where the STING activation supported by chemotherapy-induced an increase in immune surveillance through the help of exosomal NPs. Dendritic cell(DC) derived exosomes, as well as Mesenchymal stem cells (MSC), are abundantly used in immunotherapy, and hence their support can be used in chemoimmunotherapy (CIT) for multifaceted benefits.

P1598: SARS-COV2 INFECTION IN FULLY VACCINATED PATIENTS WITH LYMPHOID MALIGNANCIES DURING THE “THIRD WAVE”: A SINGLE-CENTER EXPERIENCE OF 57 PATIENTS.

Background: COVID-19-related mortality rates are increased in hematological patients and those with lymphoid malignancies look particularly vulnerable to SARS-CoV-2 infection, due to the characteristics of their disease and the anti-neoplastic treatments used. Vaccines against SARS-CoV-2 have been rapidly developed. However, patients treated with anti-CD20 monoclonal antibodies have shown lower seroconversion rates after receiving mRNA SARS-CoV-2 vaccines. Several antiviral agents, such as molnupiravir and remdesivir, and some monoclonal antibodies have been also used for the management of COVID-19 in order to reduce the risk of progression to severe disease. Aims: The aim of this study was to evaluate the outcome of SARS-Cov2 infection in a population of patients affected by chronic lymphocytic leukemia (CLL), Hodgkin lymphoma (HL), B- and T-cell non-Hodgkin lymphomas (NHLs) during the so-called “third wave” of SARS-CoV-2 pandemic. Methods: We performed a retrospective analysis of 57 patients affected by CLL (n. 12), HL (n. 8), B (n. 34) and T-cell (n. 3) NHLs who experienced SARS-CoV2 infection between December, 1, 2021, and February, 26, 2022. All patients had received a complete cycle of anti-SARS-Cov2 vaccine before infection. They were diagnosed by RT-PCR or by antigen rapid test on nasopharyngeal swabs. We collected data about sex, age, histological features, anti-neoplastic regimens, symptoms, hospitalization, mortality, use of antiviral drugs or monoclonal antibodies for the treatment of COVID-19, time to SARS-CoV-2 negativity. Results: The median age of the whole group was 58 (18-94) years. Thirty-two patients (56%) were male, while 26 (44%) were female. As far as histological features are concerned, follicular lymphoma was the most frequent one (35%). Within the last 12 months before SARS-CoV-2 infection, 40 patients (70%) had received treatment for their hematological disease, 17 (30%) were on anti-CD20 maintenance, 12 (21%) on treatment with immuno-chemotherapy (ICT), 6 (11%) on ibrutinib, 3 (5%) on checkpoint inhibitors and 3 (5%) were on chemotherapy only. All patients had received two doses of anti-SARS-CoV-2 vaccines, and 77% of them a further, booster dose. The most common symptoms at presentation were fever, cough, muscle pain, headache, fatigue. Overall, 15 (26%) patients were hospitalized, and, among them, 4 (7%) were admitted to intensive care units (ICUs). Fifteen (26%) patients received an antiviral drug, while 4 (7%) hospitalized patients received monoclonal antibodies for the treatment COVID-19. Average time length to reach a negative test for SARS-CoV-2 was 17 days. Sixteen (28%) patients remained positive after 5-to-61 days and 6 (11%) patients died. At univariate analysis, CLL and Diffuse Large B-Cell Lymphoma (DLBCL) (p 0.026), as well as treatment with ICT or BTK inhibitors (p 0.002), were significantly associated to a worse overall survival (OS). Notably, maintenance therapy with anti-CD20 monoclonal antibodies as single agents had no impact on OS. Moreover, the cumulative incidence of nasopharyngeal swabs turned negative was significantly lower in patients treated with ICT (p 0.001). Booster dose and antiviral treatments did non influence neither OS, nor time to a negative viral test. Summary/Conclusion: In our study histological subtype and type of treatment, but not antiviral therapies, had prognostic impact on the outcome of SARS COV 2 infection in patients with lymphoproliferative disorders during the current phase of pandemic. These findings warrant to be further investigated in larger series.

P651: VENETOCLAX-BASED TREATMENT OF PATIENTS WITH RICHTER SYNDROME: OUTCOMES FROM A MULTICENTER RETROSPECTIVE STUDY

Background: Patients (pts) with chronic lymphocytic leukemia (CLL) who develop Richter Syndrome (RS) have a poor prognosis with median overall survival (OS) often reported as less than 12 months (Tsimberidou JCO 2006; Rogers BJH 2018), using chemoimmunotherapy (CIT) regimens typically administered to de novo large cell lymphoma. Venetoclax (ven) has demonstrated single-agent activity in RS with an overall response rate of 43% (Davids JCO 2017). Ven combined with DA-EPOCH-R achieved a median OS of 19.6 months and the highest complete response (CR) rate (50%) reported in pts with RS (Davids Blood 2022). These results support a synergistic effect when compared to CR rates of 20% and 0% with EPOCH-R and ven monotherapy, respectively. Aims: To evaluate the outcomes of pts with RS treated with ven-based treatment, outside clinical trials, including novel-novel combinations and CIT combinations. Methods: We analyzed pts with RS treated with a ven-based regimen at MDACC (n=37) or Mayo Clinic (n=18) between 12/2013 and 8/2021. Patient and disease characteristics from the time of ven-based treatment start were ascertained. Retrospective response assessment was as per Lugano 2014 guidelines. Toxicity was recorded per iwCLL 2018 guidelines (hematologic toxicity) or CTCAE v5.0 (non-hematologic toxicity). OS and progression-free survival (PFS) were analyzed using the Kaplan-Meier method, with and without censoring for allogeneic hematopoietic stem cell transplantation (alloSCT). No formal statistical comparisons were made between different treatment groups. Results: Fifty-five pts were identified with a median age of 66 years (range 43-83 years); 31% were female. High-risk CLL disease characteristics were frequently identified: 92% unmutated IGHV, 42% del(17p), 57% TP53 mutation, and 62% complex karyotype. The median number of prior CLL-directed therapies was 2 (range 0-7), including prior chemotherapy (42%), prior Bruton tyrosine kinase inhibitor (BTKi; 38%), and prior ven (22%); 62% of pts were previously untreated for RS. Median follow-up from the start of ven-based RS treatment was 9 months (mo). The most common ven-based combination regimens achieved overall response and CR rates as follows: 50%/40% with intensive CIT + ven (n=20), 40%/30% with BTKi + ven +/- CD20 antibody (n=20), 60%/50% with R-CHOP + ven (n=10). Among the remaining 5 patients, 2 received ven monotherapy and 3 received varied ven-based combination regimens. Nine pts proceeded to subsequent alloSCT. The median PFS for the total cohort when censored at alloSCT was 4.0 mo; PFS uncensored for alloSCT was 4.4 mo (Figure 1A). Median PFS by treatment group (Figure 1B) was as follows: 3.7 mo for intensive CIT + ven, 3.9 mo with BTKi + ven +/- CD20 antibody, not reached with R-CHOP + ven. The median OS for the total cohort was 9 mo. The estimated median OS by treatment group (Figure 1C) was 8.4 mo with intensive CIT + ven, 10.6 mo with BTKi + ven +/- CD20 antibody and not reached with R-CHOP + ven. Grade 3-4 neutropenia and thrombocytopenia were more common with intensive CIT + ven (71%; 69%) and R-CHOP + ven (77%; 67%) compared to BTKi + ven +/- CD20 antibody (35%; 25%). Febrile neutropenia occurred in 42%, 33%, and 25% of pts in these three groups, respectively, with 37%, 33%, and 30% experiencing a grade 3-4 infection. Image:Summary/Conclusion: In the notoriously difficult-to-treat RS patient population, ven-based combination regimens achieve high response rates, including some with prolonged duration, particularly with the use of R-CHOP + ven. A prospective clinical trial evaluating this combination is ongoing (NCT03054896).

P1145: OUTCOMES AND TREATMENT PATTERNS AFTER FIRST RELAPSE IN PATIENTS WITH WALDENSTRÖM MACROGLOBULINEMIA

Background: Waldenström macroglobulinemia (WM) is a rare, B cell lymphoma, with a relapsing-remitting course. Despite expansion of therapeutic options, WM remains incurable. Data on outcomes of patients (pts) after first relapse or primary refractory disease are sparse. Frequently used salvage therapies include chemoimmunotherapy (CIT), proteasome inhibitor (PI) based regimens and Bruton tyrosine kinase inhibitors (BTKi). Aims: Analyze the outcomes of pts with WM after initial relapse and/or refractory (RR) disease and the impact of the type of therapy used in the second line setting. Methods: ecords of pts with WM seen at Mayo Clinic between 2000 and 2021 were reviewed. Pts with RRWM requiring second line therapy were included in the primary analysis. Response rates were assessed per the modified IWWM-6 criteria. All time to event analyses, barring progression free survival 2 (PFS2), were calculated from the start of the second line treatment, using the Kaplan Meier method. Pts were grouped based on sequence of therapy and response to frontline treatment for additional subgroup analysis. Results: Records of 220 pts with WM were reviewed; 92 had RRWM and were treated with a second line therapy. For the entire cohort, frontline regimens included dexamethasone, rituximab, cyclophosphamide (DRC) (n=93, 42%), bendamustine rituximab (BR) (n=71, 32%), bortezomib, dexamethasone, rituximab (BDR) (n=33, 15%), BTKi (n=20, 9%), and other (n=3, 1%). Median follow-up of RRWM cohort from second line therapy was 5.1 years (95% CI: 4.5-6.3). Pts with RRWM received the following therapies at first relapse: BR (n=24, 26%), BTKi (n=24, 26%), PI (n=17, 19%), DRC (n=6, 7%), autologous transplant (n=4, 4%), and other (n=17, 18%). Following second-line treatment, the overall response rate and major response rate (MRR) were 72% and 67% (CR=5%, VGPR=15%, and PR=47%), respectively. The median PFS was 2.7 years (CI: 1.7-4). 2-year overall survival (OS) rate was 87%. The median PFS2 from frontline therapy was 7.03 years (CI: 5.5-9.8). Baseline characteristics were similar for subgroups in all the following subgroup analyses. With first-line therapy, 54% of pts (n=50) achieved MRR vs. 46% (n=42) who did not. The former group had similar progression-free survival (PFS) rates as well as overall survival (OS) rates and response rates (MRR and ORR) to the second-line treatment compared to their counterparts who did not achieve MRR with the frontline regimen (Table). Thiry one pts received BTKi as either first or second line and 61 pts received no BTKi in either line. As expected, the BTKi group was enriched for pts with MYD88L265P mutation (n=29, 94%) vs 49% (n=30) in the no BTKi group, p<0.001. The outcomes between the 2 groups were comparable (Table). The group that received frontline BTKi followed by CIT/PI based Rx as second line (n=7) was compared to that receiving frontline CIT/PI based Rx followed by BTKi (n=21). The outcomes were similar (Table). Image:Summary/Conclusion: Currently available second line therapies are effective in RRWM. Achieving MRR with frontline regimen does not significantly affect overall outcomes with the second-line therapy. Although follow up is short, using a BTKi as the first- or second-line therapy appears to show comparable outcomes after second line treatment as compared to not treating with a BTKi in the upfront setting or in second-line setting. Similarly, using frontline BTKi followed by CIT as second line shares similar outcomes to treating with CIT initially followed by a BTKi. These findings require confirmation in prospective studies.

P596: CLINICAL IMPACT OF TP53 DISRUPTION IN CHRONIC LYMPHOCYTIC LEUKEMIA PATIENTS TREATED WITH A BCR INHIBITOR. A CAMPUS CLL EXPERIENCE

Background: In chronic lymphocytic leukemia (CLL), the presence of TP53 aberration (mutations and/or deletion) predicts an increased risk of relapse and death after chemo-immunotherapy (CIT). Although TP53 deletion and mutations mostly co-occur and are considered equal prognosticators, the clinical impact of isolated or concomitant mutations and deletions remains unclear in the context of targeted agents. Aims: To investigate the clinical relevance of isolated or concomitant TP53 aberrations in a large cohort of CLL patients treated with BCR inhibitors. Methods: In the framework of an institutional Italian multicenter working group on CLL (Campus CLL), a retrospective analysis of 229 CLL patients (51 treatment naïve, and 178 relapsed/refractory) treated with ibrutinib was carried out. All patients referred to a single institution for del17p analyses by FISH (167-kb 17p13 orange probe, MetaSystems) and TP53 mutations by NGS, both analyses carried out on CD19-purified (>85% pure) CLL samples within 6 months prior the start of ibrutinib treatment. The median follow-up from ibrutinib treatment was 36.3 months (95% CI 29.5-41.5 months). Overall survival (OS) and progression free survival (PFS) were computed from the start of ibrutinib treatment. Results: In the CLL cohort, 76 patients with del17p showed a trend for inferior OS respect to wt cases (P=0.0662, Fig.1A), while a significant correlation was found with PFS (P=0.0162). With regard to TP53 mutations, 296 TP53 mutations were found in 126 patients (range of mutations/patients 1-11). As with CIT, TP53-mutated patients, irrespective of VAF (Fig.1B), experienced a significantly worse OS and PFS than wt cases also by univariate analyses (P=0.0160, and P=0.0378, respectively). The combination of del17p with TP53 mutation data identified 95 cases with no TP53 aberrations, 8 cases del17p only, 58 cases TP53-mutated only, and 68 cases bearing both del17p deletion and TP53 mutation (Fig.1CD). Only patients with concomitant TP53 mutations and del17p experienced significantly shorter OS and PFS compared to TP53wt cases (P=0.0122, and P=0.0076, respectively; Fig.1CD). Conversely, patients presenting a single aberration showed no significant differences compared to wt patients (Fig.1CD). The simultaneous presence of TP53 mutations and del17p remained an independent predictor factor both for OS and PFS by multivariate analysis, together with the previous therapy lines (0-1 vs. >1), and anemia. The evolution of TP53-mutated clones was assessed by longitudinal NGS analysis of sequential PB samples collected from 38 patients (16 relapsed, and 22 on treatment) corresponding to 127 TP53 mutations. Among relapsed cases, 7 showed a prominent expansion of the TP53-mutated clone, 8 remained stable, and the remaining case displayed an evident decrease (Fig.1E). In non-relapsed patients, 3 cases presented an increase of TP53 mutations, 13 remained stable, and 6 showed a reduction (Fig.1F), with no significant difference compared to relapsed cases (P=0.0623, c2 test). BTK and PLCG2 mutations were found in 9/16 (56%) relapsed cases and in 3/22 (14%) patients still on ibrutinib (P=0.0492, c2 test). Of note, only 3/7 relapsed cases that presented a positive selection for TP53 mutations showed the presence of BTK mutations at the time of relapse. Image:Summary/Conclusion: This retrospective study indicates that only the concomitant presence of TP53 mutations and deletion is an independent negative prognostic factor for OS and PFS in patients with CLL on ibrutinib treatment; the simultaneous investigation of del17p and TP53 mutations may lead to a more precise risk assessment.

P657: REAL-WORLD TREATMENT PATTERNS OF PATIENTS DIAGNOSED WITH CHRONIC LYMPHOCYTIC LEUKEMIA (CLL) IN THE UNITED STATES (US)

Background: CLL represents the most common type of leukemia among adults in the US, but current data on the treatment patterns of patients in clinical practice is limited. Standard of care frontline therapy consists of various types of targeted therapy or chemoimmunotherapy (CIT), but it is reserved for patients with advanced-stage disease. Aims: This study aims to describe real-world treatment patterns among patients diagnosed with CLL in the US, with a focus on ibrutinib therapy. Methods: A retrospective database analysis was conducted using the Optum Clinformatics DataMartTM database (01/2007–07/2020). Patients with ≥2 medical encounters with a diagnosis code for CLL or small lymphocytic lymphoma (SLL) on different dates were selected (earliest date was defined as the index date). At least 12 months of continuous enrollment pre-index date (baseline period) and ≥18 years of age as of the index date were required. Patients with a diagnosis for mantle cell lymphoma or with evidence of anticancer therapy (antineoplastic, radiation, or cell therapy) during baseline were excluded. A subset of patients with ≥1 pharmacy claim for ibrutinib was identified. An adapted algorithm developed from previously published studies was used to identify lines of therapy (LOTs). Treatment patterns, including duration of therapy (DOT) and regimens were reported. DOT spanned from LOT initiation up to discontinuation of all agents in the LOT, a switch to another LOT, or the addition of a new agent. Median time to the first line (1L) and from 1L to second line (2L) were evaluated using a Kaplan-Meier analysis (KM) to account for censoring. Results: Among 23,087 patients with CLL, the median age was 74 years and 43% were female. Of these, 1,387 were treated with ibrutinib (median age: 75; female: 38%). Patients had a mean Charlson comorbidity index score of 1.9. Analysis of treatment patterns (Table 1) showed that 7,192 patients (31%) were treated with ≥1 LOT (mean ± standard deviation [SD] DOT of 1L: 1.6 ± 2.0 years), and 10% of patients were treated with ≥2 LOT (mean ± SD DOT of 2L: 1.2 ± 1.7 years). Ibrutinib was used by 907 patients in 1L (DOT in 1L: 1.0 ± 1.1 years) and 617 in subsequent LOTs (DOT in 2L+: 0.9 ± 1.1 years). Median time from index date to 1L initiation was 8.1 years. Of the patients who used antineoplastics therapies in 1L, a majority used CLL-related ones (79%). Most treated patients received targeted therapy (37%; rituximab: 19% and ibrutinib: 12%) and CIT (32%; bendamustine + rituximab: 13% and cyclophosphamide + fludarabine + rituximab: 5%). In 2L, 16% of patients used ibrutinib, 12% a bendamustine + rituximab regimen, and 4% chlorambucil. Median time from 1L initiation to 2L initiation was 4.4 years. Proportion of patients treated with CIT tended to diminish with subsequent LOT, whereas the proportion treated with ibrutinib tended to increase. Image:Summary/Conclusion: This real-world long-term data shows that patients receive their 1L many years after a first CLL diagnosis, with a median time to treatment of ~8 years. Among US patients with CLL, rituximab, bendamustine + rituximab, and ibrutinib were identified as the most used 1L regimens, and the latter two as the most used 2L regimens. As novel therapies are increasingly used, and genetic testing becomes more available, further research will be needed to evaluate the changes in the way CLL is treated and its effects on clinical outcomes.

PB1872: ANTIBODY RESPONSES AFTER COVID-19 VACCINATION IN PATIENTS WITH CHRONIC LYMPHOCYTIC LEUKAEMIA, EITHER TREATED OR NAÏVE. A MONOCENTRIC EXPERIENCE.

Background: The efficacy of spike messenger RNA vaccines against SARS-COV2 in immunocompetent population is about of 94-95%, while in immunocompromised patients no precise value has been established. Most of patients with Chronic Lymphocytic Leukaemia (CLL) present a consistent immunological defect, which increases the risk of mortality and morbidity from infections, including SARS-COV2. Moreover, they have shown a highly heterogeneous response to vaccination, depending on many factors including baseline features, disease and treatment status, types of therapy, vaccine administered, and immunoglobulin level at time of vaccination. Aims: We tried to evaluate the efficacy of vaccine, stratifying them according to treatment status (naïve, on treatment, off therapy) and of type of treatment, including chemo-immunotherapy (CIT), BTK or anti-Bcl2 inhibitors, monoclonal antibodies (MoAb). Methods: This monocentric study included 100 CLL patients who received two/three dose of mRNA vaccine (BNT162b2 or mRNA-1273) between January 2021 and January 2022. Median age at time of vaccination was 69 years and 51% were males. 44% patiets presented unmutated IgHv, 7% del17p, 13% del11q. 61% patients suffered significant comorbidities as hypertension, diabetes, BPCO. 71% pts received at last one prior CLL therapy, including CIT or inhibitors; 44% were actively treated at the time of vaccination. CLL treatment was not held or modified at the time of vaccination. All patents were vaccinated: BNT162b2 was administered to 80%, mRNA-1273 to 14%, two BNT162b2 and mRNA-1273 booster to 6%. Baseline demographics, treatment history and laboratory parameters including lymphocyte count and IgG levels prior to first dose of COVID-19 vaccine were collected and patients were tested for SARS-COV2 anti-spike Ig at different times from vaccination (Table 1). Results: No CLL patient experienced SARS-COV2 infection. Median IgG level at baseline was 733 mg/dL, 78% of patients had IgG levels above 500 mg/dL. At first serologic testing, at a median of 131 days after the 2nd dose, 53% patients tested negative and 47% positive. Among patients who did not develop immunity, 58% were on treatment with CIT (26%) or inhibitors, alone (62%) or in association with MoAb (12%). Among patients who developed immunity, 38% were naïve while 30% were off therapy. All patients who received MoAb in the previous six months failed to develop immunity; among patients who received MoAb from more than 6 months, 55% did not develop immunity, while 45% did. At second serologic testing, at a median of 44 days after the booster, 80% patients tested positive, with a 67% rate of seroconversion, and 20% patients tested negative (Table 1). Image:Summary/Conclusion: Our monocentric experience confirms a low humoral response in CLL, due to both disease and therapy related factors. Patients who, at the time of vaccination, were either naïve or off therapy yielded better results, probably due to a lower disease burden. The timing of MoAb administration strongly influences the response rate. Drugs that block the BTK receptors impair the humoral response of vaccination to any pathogen and behave accordingly for SARS-COV2. Data show that, in these patients, the third dose confers higher rates of response and a wider protective effect. In conclusion, vaccination is strongly recommended to all CLL patients. Due to the higher infectious risk, caused by immune dysregulation typical of CLL, it is important to evaluate the timing of vaccination and maintain safety measures at any time.

P1214: SUBCUTANEOUS EPCORITAMAB + R-CHOP FOR FIRST-LINE TREATMENT OF PATIENTS WITH HIGH-RISK DIFFUSE LARGE B-CELL LYMPHOMA: PHASE 1/2 UPDATE

Background: Patients (pts) with newly diagnosed diffuse large B-cell lymphoma (DLBCL) with high/poor risk according to the revised International Prognostic Index (IPI) who are treated with immunochemotherapy (IC) have a 4-y survival rate of 55% (Sehn et al, Blood 2007). Epcoritamab is a subcutaneously administered, well-tolerated, bispecific antibody with single-agent antitumor activity in relapsed/refractory (R/R) aggressive B-cell non-Hodgkin lymphoma (NHL). As its mechanism of action and safety profile are distinct from IC, epcoritamab is well suited for use in combination therapy and in earlier lines of therapy. The suboptimal prognosis of high-risk pts may be improved with the addition of a novel agent to standard IC. Aims: To present updated results of epcoritamab + rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP) in previously untreated pts with DLBCL and IPI 3–5 (EPCORE NHL-2 arm 1; NCT04663347). Methods: Adult pts with previously untreated CD20+ DLBCL (IPI ≥3) received subcutaneously administered epcoritamab (every wk, cycles 1–4; every 3 wk, cycles 5–6) + R-CHOP for 6 cycles of 21 d, followed by epcoritamab monotherapy (every 4 wk, in cycles of 28 d, up to 1 y). Corticosteroid prophylaxis and step-up dosing of epcoritamab were required in cycle 1 to mitigate CRS. PET-CT with contrast was used to assess response per Lugano 2014 criteria. Informed consent was obtained. Results: As of the data cutoff date of December 1, 2021, 33 pts had received epcoritamab + R-CHOP (epcoritamab 24 mg, n=4; 48 mg, n=29). Median age was 66 y (range, 19–82); median time from diagnosis to first dose of epcoritamab was 25 d (range, 5–70). At least 24% of pts had double- or triple-hit DLBCL; all had IPI ≥3. Median number of total cycles initiated was 5 (range, 1–13), and median follow-up was 3 mo (0–9.7). Among the 33 pts enrolled, 31 (94%) remained on treatment. The most common treatment-emergent adverse events (TEAEs) were neutropenia (48%; febrile neutropenia in 9% of all pts), CRS (45%), infections (42%), anemia (39%), injection-site reactions (36%), nausea (33%), constipation (30%), and pyrexia (30%). No pts discontinued epcoritamab due to TEAEs. AEs of special interest were CRS (24% grade [G] 1, 18% G2, 3% G3; resolved) and ICANS (3% G2; resolved); tumor lysis syndrome was observed in 1 pt (3% G3). Most CRS events were associated with the first full dose. Median time to resolution of CRS events was 2 d (range, 1–11); 4 pts with CRS were treated with tocilizumab. Epcoritamab was not discontinued or delayed due to CRS. There were no fatal TEAEs. Individual pt response profiles are shown in Figure 1. For efficacy-evaluable pts, irrespective of whether they had yet completed 6 cycles of therapy, the overall response rate (ORR) was 96% (24/25). Among the 10 pts who completed 6 cycles of R-CHOP and had a subsequent response assessment, the ORR and complete metabolic response (CMR) rate were 100% and 90%, respectively. These 10 pts remained in response as of the data cutoff date. The longest duration of response was 7.1+ mo and ongoing. Image:Summary/Conclusion: Epcoritamab is the first subcutaneously administered bispecific antibody to be evaluated in combination with standard IC in pts with previously untreated DLBCL. These results show that epcoritamab + R-CHOP has a manageable safety profile. CRS events were observed to be mostly of low grade and were not associated with treatment discontinuation. Rates of overall response and CMR were high, and no relapses were reported as of the data cutoff date. Updated data will be presented at the meeting.

PB2085: UPFRONT TREATMENT OF MANTLE CELL LYMPHOMA (MCL) WITH R-HDAC (RITUXIMAB-HIGH DOSE CYTARABINE + DEXAMETHASONE) IN YOUNG, HIGH RISK PATIENTS IS WELL TOLERATED AND LEADS TO DURABLE RESPONSES.

Background: MCL commonly presents as aggressive disease with a low cure rate and multiply relapsing/remitting course. Treatment of classical MCL with upfront intensive chemoimmunotherapy (CIT) consolidated with an autologous stem cell transplant (ASCT) is considered best practice in younger patients. There is no gold standard intensive CIT regimen. Common approaches include alternating RCHOP/RDHAP (Nordic) and R-Hyper-CVAD.(1) The addition of high dose Cytarabine (HDAC) has been shown to improve time to treatment failure (TTF), complete response (CR) rates and progression free survival (PFS). Aims: There is little published on the efficacy of R-HDAC in treatment-naive MCL, however a 2013 case series (Forbes et al) reported good early efficacy (CR in 16/18), with no detriment to harvest success. We describe tolerability and efficacy of upfront R-HDAC in a high risk cohort of younger patients with MCL. Methods: We identified 28 patients who received upfront R-HDAC in 3 UK centres from 2010–2021. Data were collected, anonymized and transferred centrally for analysis using Kaplan-Meier survival curves. Results: For baseline characteristics see Table 1. Treatment regimen: Dexamethasone 40mg d1-d4, Rituximab 500mg d1, Cytarabine 3000mg/m2 BD d2-d3 in 21day cycles. 22/28 (79%) completed their planned quota of 4-6cycles; 6/28 (21%) did not. Of these n=5 had progressive disease (PD), n=1 ceased with toxicity. 4/28 incurred cycle delays. 1 patient developed PD after completing R-HDAC. Haematological toxicity ≥ Grade 3 CTCAE: Anaemia 71%; Thrombocytopenia 93%; Neutropenia 93%. Fatigue (57%), Nausea 25%, Vomiting 7%, Constipation 21%, Diarrhoea 11%, Cardiac toxicity 11%, Pulmonary toxicity 18%, Rash 11%. 20/28 (71%) underwent stem cell transplant consolidation of which 19 had an ASCT. The median CD34+ stem cell harvest was 8.3x109^L/Kg (2.56-40.9) with no harvest failures. One patient underwent an allogeneic SCT. Of those who didn’t undergo transplant: 1/8 declined; 1/8 was ineligible; 6/8 had PD and switched to 2nd line therapy. Overall Response Rate (ORR) (RECIST) was 78%, CR 41%; PR (Partial response) 37%; and PD 22%. The median PFS was 3.39years (95% CI 0-7.937). 5y OS was 64.3% (95% CI 44.9-83.7%), median OS 8.7years (95% CI 2.634 – 14.894). Image:Summary/Conclusion: Our cohort showed higher rates of haematological toxicity, but lower gastrointestinal toxicity than those reported with the Nordic approach.(1) There were no incidents of treatment related mortality (TRM). More intensive regimens e.g. R-Hyper-CVAD have documented TRM rates of up to 8%. Only 1 patient in our cohort ceased treatment because of toxicity. Whilst our ORR is lower than those published in trial data on commonly used regimens (78% vs MCL Younger trial ORR: RCHOP arm 90%/Cytarabine arm 94%) our cohort’s baseline demographics are comparably much higher risk: MIPIb High 53% vs 25/20%; Blastoid disease 25% vs 9/8%. Of those with PD in our cohort, 4/6 had high MIPIb and blastoid disease. Despite this disparity, R-HDAC retains a comparable CR rate (41% vs 38%) and 5y OS (64.3% vs 65%). Whilst this observational retrospective study has limitations, it has shown that R-HDAC is an option for younger patients with high risk MCL. Using fewer CIT drugs could reduce toxicity and reserve more agents for use in future relapse.

P664: GRADING QUALITY OF EVIDENCE AND STRENGTH OF RECOMMENDATIONS FOR THE TREATMENT OF RELAPSED/REFRACTORY CLL.

Background: Changes in the treatment landscape of CLL have complicated the decision-making processes, especially in the context of relapsed/refractory (R/R) disease. In this setting current guidelines do not provide clear information on the sequencing of targeted agents (TAs). Aims: With this in mind a series of evidence-based recommendations were produced to support pts, clinicians, and other health care professionals in their decisions about the management of R/R CLL. Methods: A multidisciplinary panel that included specialists in methodology, CLL management, and hematology, performed a systematic review of the literature using the databases MEDLINE, EMBASE, and the Cochrane Library, then participated in a virtual consensus conference held at the end of December 2021. The Grading of Recommendations Assessment, Development, and Evaluation (GRADE) approach was used to formulate recommendations. Specifically, the strength of recommendations was determined by the balance between desirable and undesirable consequences of alternative management strategies, quality of evidence, variability in values, preferences, and resource used. Results: Firstly, the panelists prioritized 10 scientific questions in the context of 4 specific scenarios of R/R CLL: (1) relapse after frontline chemo-immunotherapy (CIT), (2) progression of disease (PD) while receiving ibrutinib (IBR), (3) progression after treatment with venetoclax (VEN), and (4) impact of adherence to IBR or VEN on the clinical outcome. The following recommendations were produced: 1- A TA should be offered to all pts relapsing after first-line CIT (strong recommendation based on high-quality evidence). In absence of head-to-head trials comparing a BTKi vs an anti-BCL2 inhibitor, the panel suggests a patient-oriented choice consisting of either continuous BTKi (i.e., IBR or acalabrutinib) or time-limited (TL) VEN-based therapy in both standard or high genomic risk (conditional recommendation based on moderate-quality evidence). Remarks: TL VEN-based regimen is more cost-effective than continuous IBR. 2- The panel recommends switching to VEN for those pts who experience PD whilst on a BTKi (in absence of a valid alternative the recommendation becomes strong even if the quality evidence is moderate). There is no evidence to recommend the combination of VEN plus rituximab or an alternative covalent BTKi over VEN single agent (conditional recommendation based on low certainty in the evidence of effects). Noncovalent BTKi pirtobrutinib needs validation in phase 3 studies. 3- The panel recommends utilizing a BTKi monotherapy instead of re-challenging VEN for pts who have progressed after completing VEN-based therapy (conditional recommendation based on low certainty in the evidence of effects). 4- Finally, panelists agreed that the impact of adherence to IBR or VEN on PFS in R/R pts is supported by a low quality of evidence (conditional recommendation based on low certainty in the evidence of effects). Summary/Conclusion: These evidence-based consensus recommendations strongly support the use of a TA in R/R CLL patients. The choice between TL and continuous TA is patient-oriented with the remark that a TL approach is cost-effective within current pricing structures. A cross-over approach to an alternative TA is suggested in pts progressing on BTKi or BCL2i. However, these recommendations are guided by the fundamental principle that optimal patient care involves ongoing discussions between clinicians and pts, continuously addressing goals of care and the relative risk-benefit balance of treatment.

P1168: CHARACTERISTICS PREDICTIVE OF PROGRESSION DURING FRONTLINE TREATMENT IN AGGRESSIVE B-CELL LYMPHOMAS

Background: Primary refractory diffuse large B-cell lymphoma (DLBCL) represents 10-15% of DLBCL cases. The subgroup of refractory patients who have no response or progressive disease (PD) by the end of frontline treatment (EOT) is a high-risk group with particularly poor outcomes. It is challenging to identify such patients at diagnosis. Aims: To identify clinical, pathological, and cytogenetic characteristics of patients with progression during frontline treatment. Methods: Adult patients with newly diagnosed DLBCL, including patients with high-grade B-cell lymphoma with MYC and BCL2 and/or BCL6 rearrangements (DHL/THL), between 2002 and 2019 and seen at Mayo Clinic Rochester were identified from the prospective Molecular Epidemiology Resource (MER) cohort study of the University of Iowa/Mayo Clinic Lymphoma SPORE. We analyzed patients who had no response or PD during treatment or by EOT (early PD group) and compared to non-early PD (non-ePD) patients (including relapsed patients). We compared demographics, clinical characteristics, cell of origin (COO), and MYC rearrangements using Chi-square analysis. Results: Out of 1,505 patients with DLBCL, there were 66 patients (4.3%) with early PD (N=20 PD/stable disease at interim PET-CT, N=46 PD by EOT). At baseline, 61% were male and the median age was 60. Early PD patients had more advanced stage III-IV (72.7% vs 53.3%), elevated serum lactate dehydrogenase (LDH) (64.0% vs 47.3%), >1 extranodal site involved (36.4% vs 23.3%), and International Prognostic Index (IPI) ≥3 (52.0% vs 33.6%)(all p <0.05 compared to non-ePD). COO distribution was similar between early PD and non-ePD patients. Among patients with complete pathological and cytogenetic data available (early PD, n=47; non-ePD, n=813), DHL or THL was observed in 23.4% of early PD patients compared to 9.2% in non-ePD patients (p=0.001). Of the DHL patients in the early PD group (n=8), MYC/BCL2 rearrangement was present in 87.5%, MYC/BCL6 in 12.5%. Dual Myc/Bcl2 expressor (DEL) was present in 42.2% of early PD patients (n=45) compared to 25.5% in non-ePD patients (n=736)(p=0.013). First-line treatment regimens in the early PD group included R-CHOP (74.2%), R-EPOCH (7.6%), and other immunochemotherapy (IC)(18.2%), which was similar to non-ePD patients. Summary/Conclusion: High-risk characteristics including DHL/THL and DEL are significantly associated with progressive disease during frontline treatment, suggesting that MYC-signaling may mediate chemoresistance. Known high-risk clinical features including advanced stage, elevated LDH, >1 extranodal site, and IPI ≥3 are also associated with early PD. Early identification of patients at high risk for early PD through clinical, pathological, and cytogenetic features is of utmost importance given the availability of clinical trials incorporating novel therapies in both frontline and consolidative approaches.

Progression-Free Survival at 24 Months as A Landmark After Autologous Stem Cell Transplant in Relapsed or Refractory Diffuse Large B-cell Lymphoma

Patients with newly diagnosed diffuse large B-cell lymphoma (DLBCL) who achieve progression-free survival (PFS) at 24 months (PFS24) after immunochemotherapy (IC) have excellent overall survival (OS) comparable to that of the age- and sex-matched general population. However, a similar landmark has not been established for patients with relapsed or refractory (RR) DLBCL following frontline IC who are subsequently treated with salvage therapy followed by autologous stem cell transplantation (ASCT). To evaluate the role of PFS24 as a landmark after ASCT in patients with RR DLBCL, we identified patients with RR DLBCL after frontline R-CHOP or R-CHOP-like IC who underwent salvage therapy and ASCT at Mayo Clinic between July 2000 and December 2017 and University of Iowa between April 2003 and April 2020 from institutional lymphoma and transplantation databases. Clinical characteristics, treatment information, and outcome data were abstracted. PFS, OS, and post-ASCT relapse survival (PRS) were analyzed using Kaplan-Meier method, and cumulative incidences of relapse versus nonrelapse mortality and different causes of death were compared accounting for competing events. A total of 437 patients were identified. Median age at ASCT was 61 years (range 19-78), and 280 (64%) were male. After a median post-ASCT follow-up of 8.0 years (95% confidence interval [CI], 7.2-8.7), 215 patients had a relapse (or disease progression), 180 within 2 years and 35 after 2 years. For the entire cohort, the post-ASCT relapse rate was much higher than the nonrelapse mortality rate (48.1% versus 9.1% at 5 years). Median PFS and OS after ASCT was 2.7 and 5.4 years, respectively. Lymphoma was the primary cause of death after ASCT. In contrast, for patients who had achieved PFS24 (n = 220), rates of post-PFS24 relapse and nonrelapse mortality were similar (14.8% and 12.3% at 5 years). Median PFS and OS after achieving PFS24 was 10.0 and 11.5 years, respectively. Lymphoma-related and -unrelated death rates were similar after achieving PFS24. For all patients who had a post-ASCT relapse, median PRS was 0.7 (95% CI, 0.5-0.9) year, and late relapse (>2 versus ≤2 years after ASCT) was associated with better PRS (median 2.3 [1.7-4.8] versus 0.5 [0.3-0.7] years, P< .001). The study establishes PFS24 as an important landmark associated with post-ASCT outcomes in patients with RR DLBCL after frontline IC.

Brief Report: A Blood-Based MicroRNA Complementary Diagnostic Predicts Immunotherapy Efficacy in Advanced-Stage NSCLC With High Programmed Death-Ligand 1 Expression

IntroductionPatients with advanced, non-oncogene-driven NSCLC with high programmed death-ligand 1 (PD-L1) expression are eligible for treatment with immunotherapy. There is, however, an urgent medical need for biomarkers identifying cases that require additional combination with chemotherapy. We previously uncovered a myeloid-based 5-microRNA (miRNA) signature that identified responders to immunotherapy in PD-L1 unstratified patients; however, its potential utility in treatment guidance for patients with PD-L1 high tumors remained unclear. MethodsWe trained (n = 68) and validated (n = 56) a 5-miRNA multivariable Cox proportional hazards model predictive of overall survival on small RNA sequencing data of whole blood samples prospectively collected before the commencement of immunotherapy for stage IV NSCLC with PD-L1 tumor proportion score greater than or equal to 50%, treated with PD-1 inhibitor monotherapy (immunotherapy alone [IO]). Specificity was demonstrated in a control cohort treated with immunochemotherapy (ICT) (n = 31). ResultsThe revised 5-miRNA risk score (miRisk) stratified IO-treated patients and identified a high-risk group with significantly shorter overall survival (hazard ratio = 5.24, 95% confidence interval: 2.17–12.66, p < 0.001). There was a significant interaction between the miRisk score and type of treatment (IO or ICT, p = 0.036), indicating that the miRisk score may serve as a predictive biomarker for immunotherapy response. Furthermore, the miRisk score could identify a group of high-risk patients who may benefit from treatment with ICT as opposed to IO (hazard ratio = 0.35, 95% confidence interval: 0.15–0.82, p = 0.018). ConclusionsThe miRisk score can distinguish a group of patients with PD-L1 high, stage IV NSCLC likely to benefit from adding chemotherapy to immunotherapy and may support treatment decisions as a blood-based complementary diagnostic.

Prognostic role of neutrophil-to-lymphocyte ratio and EPSILoN score in advanced non-small-cell lung cancer patients treated with first-line chemo-immunotherapy.

Background: Clinical and laboratory biomarkers in patients withadvanced non-small-cell lung cancer (aNSCLC) receiving chemo-immunotherapy (CIT) are still poorly explored. Materials & methods: All consecutive aNSCLC patients who received at least one cycle of first-line CIT were enrolled. The impact of several clinical and laboratory biomarkers on outcomes was evaluated through Cox proportional hazard models. Results: Higher neutrophil-to-lymphocyte ratio was shown to be an independent prognostic biomarker of both worse progression-free survival and worse overall survival. The EPSILoN score was able to divide patients into three different prognostic groups, with a median overallsurvival of 73.2, 45.6 and 8.6months for the favorable, intermediate and poor groups, respectively. Conclusion: The neutrophil-to-lymphocyte ratio and EPSILoN score were shown to have a prognostic value in aNSCLC patients treated with CIT.

Abstract 3480: Quantitative assessment of the evolution of therapeutic target antigen expression in diffuse large b-cell lymphoma in response to treatment

Abstract Introduction: Variability in expression of B-cell surface antigens could be an important mechanism of treatment failure after immunotherapy in patients with relapsed or refractory (R/R) diffuse large B-cell lymphoma (DLBCL). Understanding the evolution of target antigen expression can guide selection and sequencing of newer therapies targeting CD19 and CD20. We sought to quantitate the change in expression of CD19 and CD20 in R/R DLBCL after Rituximab (R)-based chemo immunotherapy (CIT) relative to pretreatment levels. Methods: Pts. diagnosed with DLBCL after January 2014 who were R/R to R-based CIT (R-CHOP or R-EPOCH), were identified and clinical variables at diagnosis (Dx) and first R/R were recorded. Data from archival flow cytometry assays on Dx and R/R biopsies were accessed. Using FCS Express® software, neoplastic cells were gated, and fluorescence intensity (FI) of CD19 and CD20 expression were reported. Multivariate linear mixed model was used to compare median and geometric mean FI of CD19 and CD20 between Dx and R/R. Results: A total of 51 flow cytometry assays (26 Dx and 25 R/R) were analyzed for 33 pts., of whom paired assays (at both Dx and R/R) were available for 18 pts. Median age at Dx was 64 (range, 41-76) yrs, 24 pts. (73%) were male and 29 (88%) had IPI ≥ 2. Cell of origin at Dx was GCB in 16 (49%), non-GCB in 12 (36%) pts., while two had a double-hit rearrangement. Median time to R/R was 10.4 months. There was a significant reduction in median FI of CD20 from Dx [median: 40,610 (range: 167 - 259,962)] to R/R [median: 11,596 (range: 63 - 79,592)], representing a reduction of 63% at R/R relative to Dx (P= 0.01; 95% CI: 20-73%). Similar change was observed in geometric mean FI of CD20, which was reduced 65% at R/R relative to Dx (P&amp;lt; 0.01; 95%CI: 31-82%). Median and geometric mean FI of CD19 at R/R were 38% and 20% lower compared to Dx, respectively, but these differences were not statistically significant (P= 0.08 and 0.39, respectively). Relative change in FI at R/R in individual cases, compared to the mean FI of all Dx cases, showed that 21 out 25 R/R cases (84%) had reduction of CD20 whereas only 14/25 (56%) had reduction of CD19. Interestingly, 7/25 (28%) R/R cases had an increase in CD19 expression by &amp;gt;80%. Reduction in CD20 geometric mean FI from Dx to R/R was significantly associated with age &amp;gt;60 years (p=0.04), bone marrow involvement (p &amp;lt;0.01) and &amp;gt;1 site of extra nodal involvement (p= 0.03) at Dx. Conclusions: Quantitative assessment by flow cytometry revealed a significant decline in expression of CD20 at R/R compared to Dx in patients with DLBCL treated with R-based CIT. CD19 expression was largely unchanged, although dramatically upregulated in a subset of R/R cases. Given the role of CD19 mediated pathways in B-cell NHL and its association with PI3K pro-survival signaling, these data merit further exploration as a potential mechanism of treatment resistance. Citation Format: Agrima Mian, Narendra Bhattarai, Wei Wei, Manishkumar S. Patel, Paolo F. Caimi, Sarah L. Ondrejka, Brian T. Hill. Quantitative assessment of the evolution of therapeutic target antigen expression in diffuse large b-cell lymphoma in response to treatment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3480.