Including Objective Response Rate Research Articles

Impact of chemotherapy on patients with mismatch repair deficient advanced endometrial carcinomas-a meta-analysis.

Chemo-immunotherapy is standard of care for women with recurrent or advanced mismatch repair deficient (dMMR) endometrial carcinomas (EC). However, it is uncertain whether patients with dMMR advanced or recurrent EC derive less benefit from chemotherapy than those with mismatch repair proficient (pMMR) EC. We performed a meta-analysis of randomized controlled trials (RCTs) in advanced/recurrent EC to determine the difference in the benefit of chemotherapy in dMMR vs pMMR EC. Data on chemotherapy outcomes including objective response rate (ORR), progression-free survival (PFS) and overall survival (OS) were retrieved. We pooled these data using the inverse variance method and examined subgroup difference by MMR status. We also compared differences in PFS and OS outcomes by creating individual patient data from the Kaplan-Meier curves of trial publications for sensitivity analyses. A total of five RCTs with 1137 participants (dMMR, 26%; pMMR, 74%) were included. All participants were treated with carboplatin-based chemotherapy. There was no difference between the dMMR and pMMR subgroups for ORR (66.5% vs 64.0%, P = .20 for subgroup difference), PFS (HR 0.93, 95% CI 0.77-1.12, P = .44; median PFS 7.6 vs 9.5 months) or OS (HR 1.03, 95% CI 0.73-1.44, P = .88; median OS not reached vs 28.6 months). ORR, PFS and OS were similar among those with dMMR vs pMMR endometrial cancer treated with front-line, platinum-doublet chemotherapy in randomized clinical trials. These findings reinforce the importance of combining chemotherapy together with immune checkpoint inhibitors until the results of trials comparing immune checkpoint therapy alone with combination therapy are available.

Paraneoplastic neurological syndrome and its impact on the treatment outcomes of small-cell lung cancer: A single-center retrospective analysis.

Paraneoplastic neurological syndrome (PNS) is associated with small-cell lung cancer (SCLC). However, the frequency and characteristics of PNS and the efficacy of anticancer treatment for these patients have not been investigated in the Japanese/Asian population previously. Therefore, we aimed to better understand PNS by evaluating real-world data from patients with PNS complicated by SCLC. Patients diagnosed with Stage II-IV SCLC at a single center between August 2007 and April 2021 were retrospectively analyzed. The primary outcome was the incidence of PNS. The secondary outcomes were the change in performance status (PS) after treatment commencement and outcomes following anticancer treatment, including objective response rate (ORR), progression-free survival (PFS), and overall survival (OS). A total of 318 patients were evaluated; PNS was present in 2.8% (n = 9) of the overall population. All patients with PNS exhibited poor Eastern Cooperative Oncology Group PS (≥2); moreover, 78% of patients had a PS score of 3-4. An improvement in PS was observed in 56% (n = 5) of patients. Patients with PNS exhibited treatment efficacies similar to patients without PNS (ORR: 89% vs. 83%, p = 1.0; PFS: 7.6 vs. 5.7 months, p = 0.69; OS: not reached vs. 15.6 months, p = 0.23). A total of 2.8% of patients had SCLC complicated by PNS, with poor PS observed. However, anticancer therapy led to an improvement in PS and comparable ORR, as well as PFS and OS similar to those observed in patients without PNS. Thus, anticancer therapy should be considered in patients with PNS.

Efficacy of immunotherapy in RET fusion-positive NSCLC: A meta-analysis

BackgroundThe Rearranged during Transfection (RET) gene represents a rare driver mutation in non-small cell lung cancer (NSCLC) occurring in only 1 %–2 % of cases, with implications in targeted carcinogenesis. Despite the significant efficacy demonstrated by immunotherapy in advanced NSCLC with wild-type driver genes, its validation in RET fusion-positive patients is yet to be established. ObjectivesThis meta-analysis aims to systematically evaluate the effectiveness of immunotherapy in patients with RET fusion-positive NSCLC. Data sourcesand Methods: PubMed and Web of Science databases were systematically searched for relevant studies. Outcomes including objective response rate (ORR), disease control rate (DCR), progression-free survival (PFS), and overall survival (OS) were extracted for further analysis. ResultsTen real-world evidence (RWE) studies involving 7145 patients were enrolled in this meta-analysis. In terms of tumor response, the pooled ORR and DCR were 24.0 % and 61.0 %, respectively. Regarding survival analysis, the pooled median PFS and median OS were 4.17 months [95 % confidence interval (CI): 3.40–5.02) and 17.22 months (95 % CI: 11.58–23.91)], respectively. Subgroup analyses showed that immunotherapies plus chemotherapy were superior to single-immunotherapy in terms of ORR, DCR, and median PFS, which were 43 % (95 % CI: 31%–55 %) vs. 17 % (95 % CI: 11%–25 %), 74 % (95 % CI: 60%–84 %) vs. 45 % (95 % CI: 31%–59 %) and 6.69 months (95 % CI: 4.91–8.93) vs. 2.96 months (95 % CI: 2.25–3.78), respectively. ConclusionsTo date, RET fusions appear to be associated with poor response to immunotherapy in NSCLC patients, and immunotherapy combined with chemotherapy seems to offer greater clinical benefits than mono-immunotherapy.

Safety and efficacy of restarting immune checkpoint inhibitors in non-small cell lung cancer patients following immune-related adverse events: a systematic review and meta-analysis.

This meta-analysis aims to evaluate the safety and efficacy of restarting immune checkpoint inhibitors (ICIs) in patients with non-small cell lung cancer (NSCLC) after experiencing immune-related adverse events (irAEs). A comprehensive search of PubMed, Web of Science, Embase, and the Cochrane Library was conducted to identify studies investigating the safety and efficacy of restarting ICIs in NSCLC patients after irAEs. Outcome measures, including objective response rate (ORR), progression-free survival (PFS), and overall survival (OS) after ICI restarting, were extracted. Meta-analysis was performed using the R meta-package. Four studies involving a total of 326 subjects were included, comprising 137 patients who restarted ICI treatment after irAEs and 189 patients who did not restart ICI treatment. The results revealed that ICI restarting was associated with an increased ORR (OR = 2.36, 95% CI 1.49-3.84), prolonged PFS (HR = 0.60, 95% CI 0.42-0.86), and prolonged OS (HR = 0.65, 95% CI 0.43-0.99) compared to non-restarting. The incidence of irAEs after ICI restarting was 45% (95% CI 0.27-0.63). Restarting ICI treatment after discontinuation due to previous irAEs appears to be a reasonable option for NSCLC patients. However, a comprehensive assessment of the potential benefits and risks to individual patients is crucial, and close monitoring of irAEs is warranted.

Safety and preliminary efficacy results of IBI389, an anti-CLDN18.2/CD3 bispecific antibody, in patients with solid tumors and gastric or gastro-esophageal tumors: A phase 1 dose escalation and expansion study.

2519 Background: CLDN18.2 expression has been observed in various solid tumors especially in gastric cancer, indicating its potential as a novel target for anti-tumor therapy. IBI389 is an anti-CLDN18.2/CD3 bispecific antibody that induces immune synapse formations by linking CD3 molecules in T-cell receptor complexes and CLDN18.2 antigens on the membrane of tumor cells. Herein, we report preliminary results from a phase I study to evaluate safety and efficacy of IBI389 in patients (pts) with advanced solid tumors. Methods: Eligible pts with advanced solid tumors who failed or were intolerant to standard treatments were enrolled. The dose escalation of IBI389 monotherapy used intra-patient dose escalation with accelerated titration and the classic 3+3 design (0.003 µg/kg to 600 µg/kg). Selected dose levels were expanded in pts with advanced gastric/gastroesophageal junction cancer (G/GEJ C) and pancreatic ductal adenocarcinoma (PDAC). The primary objective was safety. Secondary objective was efficacy assessed by investigator per RECIST v1.1 including objective response rate (ORR) and disease control rate (DCR). Results: As of January 9, 2024, a total of 114 pts were enrolled (males: 67.5%, median age: 60.0 years, G/GEJ C: 32.5%, PDAC: 57.9%, stage IV: 81.6%). No dose-limiting toxicity (DLT) was observed during dose escalation. The MTD was not reached. In all pts, treatment-emergent adverse events (TEAEs) occurred in 112 (98.2%) pts including 76 (66.7%) pts with grade ≥3 TEAEs. Treatment-related adverse events (TRAEs) occurred in 111 (97.4%) pts including 63 (55.3%) pts with grade ≥3 TRAEs. The most common grade ≥3 TRAEs (≥ 4%) were gamma-glutamyl transferase increased (21.9%), lymphocyte count decreased (13.2%) and nausea (4.4%). Cytokine release syndrome (CRS) related adverse events occurred in 65 (57.0%) pts including 1 (0.9%) pts with grade 3 CRS and no grade 4 or 5 CRS. TEAEs leading to dose interruption and treatment discontinuation occurred in 44 (38.6%) and 8 (7.0%) pts. Preliminary efficacy of IBI389 was observed in pts with CLDN18.2 expression ≥10% (immunohistochemistry 2+/3+). In G/GEJ C pts with previous treatments ≥2 lines receiving IBI389 at various dose levels ranging from 10µg/kg to 600 µg/kg (n=26), 8 pts had partial response (PR) and 11 pts had stable disease (SD). The ORR was 30.8% (95%CI: 14.3-51.8) and DCR was 73.1% (95%CI: 52.2-88.4). Conclusions: IBI389 showed manageable safety profiles in pts with advanced solid tumors and preliminary efficacy in CLDN18.2-positive pts with G/GEJ C. Clinical trial information: NCT05164458 .

PRIMROSE: A modular phase 1/2a study of AZD3470, an MTA-cooperative PRMT5 inhibitor, in patients with MTAP deficient advanced solid tumors.

TPS3179 Background: Protein arginine methyltransferase 5 (PRMT5) is an epigenetic enzyme that catalyzes symmetric dimethylation of arginine substrates, regulating multiple cell processes. Deletion of the methylthioadenosine phosphorylase gene MTAP in tumor cells results in accumulation of the metabolite methylthioadenosine (MTA), a partial inhibitor of PRMT5, potentially rendering tumor cells susceptible to further PRMT5 targeting. Clinical activity of first-generation, non-selective PRMT5 inhibitors (PRMT5i) is limited by bone marrow toxicity due to lack of selectivity between normal cells and MTAP-deficient tumor cells. Second-generation PRMT5i, including AZD3470, should selectively target MTAP-deficient tumor cells whilst sparing normal cells. AZD3470 preferentially binds PRMT5 in the presence of MTA in MTAP-deficient tumor cells, inhibiting PRMT5 methylation activity, and is less effective in MTAP-proficient cells. PRIMROSE (NCT06130553) is a first-in-human, Phase 1/2a, open-label, multicenter study of AZD3470 as monotherapy and in combination with anti-cancer agents in patients with MTAP-deficient advanced / metastatic solid tumors. Methods: Eligible patients are aged ≥18 years with MTAP-deficient advanced or refractory solid tumors, ≥1 prior line of treatment in the recurrent / metastatic setting, ≥1 measurable lesion per RECIST v1.1, ECOG performance status 0/1, adequate organ and bone marrow function, and no prior treatment with PRMT5i. Module 1 will evaluate AZD3470 monotherapy. Part A (dose escalation) will enroll up to ~54 patients and follow a modified toxicity probability interval-2 (mTPI-2) design with once-daily dosing in 21-day cycles. Treatment will be given until progression or discontinuation criteria are met. Part B (dose optimization and expansion) will expand specific patient populations and / or tumor types, with up to ~30 patients per cohort; dosing will be based on safety and tolerability data from Part A. Further modules for combination treatments may be added based on emerging supportive data. The primary objectives are to assess safety and tolerability, including dose-limiting toxicities, and to determine the recommended phase 2 dose of AZD3470. The secondary objective is evaluation of efficacy, including objective response rate, duration of response, disease control rate, change in tumor size, progression-free survival, and overall survival. An additional secondary objective in Module 1 is to assess pharmacokinetics. The study is planned to take place in ~20 centers across eight countries. The study was opened to enrollment in December 2023. Clinical trial information: NCT06130553 .

First-in-class PD-1/IL-2 bispecific antibody fusion protein IBI363 in patients with advanced melanoma: Safety and efficacy results from a phase I study.

9562 Background: Despite great success of immunotherapy (IO) in advanced melanoma, there remains unmet clinical needs for IO resistant and cold tumors. IBI363 is a first-in-class PD-1/IL-2α-bias bispecific antibody fusion protein which could block PD-1 checkpoint and activate α-bias IL-2 to rejuvenate exhausted tumor-specific T cells. Herein, we report updated results from the phase I study to evaluate safety and efficacy of IBI363 in pts with advanced melanoma. Methods: Eligible pts with advanced melanoma who failed or intolerant to standard therapy were enrolled to receive IBI363 intravenously at different dose levels ranging from 100-2000 μg/kg QW/Q2W/Q3W. Primary objective of the study was safety. Secondary objective was efficacy assessed by investigator per RECIST v1.1 including objective response rate (ORR), disease control rate (DCR), duration of response (DoR) and progression free survival (PFS). Results: As of January 11, 2024, 67 pts were enrolled (females: 55.2%, median age: 59.0 years, ECOG PS 1: 74.6%, prior treatment lines ≥2: 59.7%, prior IO: 89.6%). There were 17 pts with cutaneous melanoma, 22 pts with acral melanoma, 25 pts with mucosal melanoma and 3 pts with unknown primary melanoma. The median treatment duration was 12.0 weeks (range: 2.0-43.6) with 38 pts (56.7%) still on treatment. Most comment reason for end of treatment was disease progression in 25 pts (37.3%). All pts were included in safety analysis. Treatment-emergent adverse events (TEAEs) occurred in 63 (94.0%) pts. Grade ≥3 TEAEs and TRAEs occurred in 16 (23.9%) and 12 (17.9%) pts. Common TEAEs (≥20%) were arthralgia (34.3%), hyperthyroidism (29.9%), anemia (25.4%). TEAE leading to treatment discontinuation occurred in 1 (1.5%) pt.No pts had TEAEs leading to death. Pts with at least 1 post-baseline tumor assessment were included in efficacy evaluable set. In all evaluable pts (n=57), the best overall response was partial response (PR) in 16 pts, stable disease (SD) in 25 pts and progressive disease (PD) in 16 pts. The overall ORR was 28.1% (95%CI: 17.0-41.5%) and DCR was 71.9% (95%CI: 58.5-83.0). In pts had prior IO (n=52), ORR was 21.2% (95%CI: 11.1-34.7) and DCR was 67.3% (95%CI: 52.9-79.7). In 1 mg/kg Q2W pts had prior IO (n=25), ORR was 32.0% (95%CI: 14.9-53.5) and DCR was 80.0% (95%CI: 59.3-93.2). The DoR and PFS data were immature at the time of analysis. Biomarker analysis in baseline tumor region observed significantly higher CD8 T cell infiltration (measured by cell positivity and density) in PR/SD patients than PD patients (p<0.05). More updated data on safety and efficacy will be presented at the meeting. Conclusions: In pts with advanced melanoma, IBI363 showed encouraging efficacy in different tumor subtypes and in pts wit prior IO. The safety profiles were acceptable and manageable. Further clinical development of IBI363 in melanoma are ongoing both in China and overseas. Clinical trial information: NCT05460767 .

Safety and efficacy of IBI389, an anti-CLDN18.2/CD3 bispecific antibody, in patients with advanced pancreatic ductal adenocarcinoma: Preliminary results from a phase 1 study.

4011 Background: CLDN18.2 expression has been observed in various solid tumors. In pancreatic ductal adenocarcinoma (PDAC), positive CLDN18.2 expression was reported in nearly 60% patients (pts), indicating its potential as a novel target for anti-tumor therapy. IBI389 is an anti-CLDN18.2/CD3 bispecific antibody that induces immune synapse formations by linking CD3 molecules in T-cell receptor complexes and CLDN18.2 antigens on the membrane of tumor cells. Herein, we report preliminary result from a phase I study to evaluate safety and efficacy of IBI389 in pts with PDAC. Methods: EligibleCLDN18.2-positivepts with locally advanced, refractory or metastaticPDAC who failed or were intolerant to standard treatments were enrolled. IBI389 monotherapy was intravenously administered at 6 dose levels (5-600 µg/kg, Q3W or Q2W) during the 2-stage dose escalation and the dose expansion. In dose levels ≥ 30 µg/kg, the step-up dosing strategy with priming dose of 3 to 10 µg/kg was applied. The primary objective was safety. Secondary objective was efficacy assessed by investigator per RECIST v1.1 including objective response rate (ORR) and disease control rate (DCR). Results: As of January 9, 2024, a total of 64 CLDN18.2-positive PDAC pts were enrolled (males: 64.1%, females:35.9%, median age: 60.0 years, stage IV: 84.4%). All patients received prior therapy with a median of 2 lines (range: 1 to 5). Treatment-related adverse events (TRAEs) occurred in 62 (96.9%) pts including 35 (54.7%) pts had grade ≥3 TRAEs. The most common grade ≥3 TRAEs (≥5%) were gamma-glutamyl transferase increased (20.3%), lymphocyte count decreased (9.4%) and nausea (7.8%). Cytokine release syndrome (CRS) related adverse events occurred in 33 (51.6%) pts with no grade ≥3 CRS occurred. TEAEs leading to dose interruption and treatment discontinuation occurred in 24 (37.5%) and 3 (4.7%) pts. Preliminary efficacy of IBI389 was observed in pts with CLDN18.2 expression ≥10% (immunohistochemistry 2+/3+) at 600 µg/kg. As of January 31, 2024, there were 23 evaluable pts including 7 pts with PR and 9 pts with SD. The ORR was 30.4% (95%CI: 13.2-52.9) and DCR was 69.6% (95%CI: 47.1-86.8). The median duration of response (DoR) and progression-free survival (PFS) was not reached. More updated data on safety and efficacy will be presented at the meeting. Conclusions: IBI389 showed manageable safety profiles in pts with advanced PDAC. Preliminary efficacy was observed, including in pts with relatively low expression of CLDN18.2. Clinical trial information: NCT05164458 .

H3B-6545 in women with locally advanced/metastatic estrogen receptor-positive (ER+), HER2 negative (–) breast cancer (BC).

1015 Background: H3B-6545 is a novel selective ER covalent antagonist (SERCA) that inactivates wild-type and mutant ERα. This phase 1/2 study aimed to identify the maximum tolerated dose (MTD)/recommended phase 2 dose (RP2D), and characterize safety and efficacy of H3B-6545 in women with advanced/metastatic ER+, HER2– BC. Methods: This multicenter, open-label study included dose-escalation [ph1] and -expansion [ph2] phases. Females (postmenopausal or concurrently receiving a luteinizing hormone-releasing hormone agonist) with ER+, HER2–BC who had disease progression on standard therapy were eligible. Prior therapy must have included a minimum of 2 hormonal therapies (HTs), or 1 HT + 1 chemotherapy, or 1 HT + a CDK4/6 inhibitor. H3B-6545 was administered orally QD at doses of 100-600 mg. The MTD was the highest dose at which ≤1 of 6 patients (pts) had a dose-limiting toxicity (DLT). In ph2, efficacy of the RP2D was examined. The primary endpoints were determination of RP2D (ph1) and efficacy (ph2; including objective response rate [ORR], duration of response [DOR], and progression-free survival [PFS] per RECIST v1.1 by investigator, and overall survival [OS]). Safety and PK were secondary endpoints. Results: At data cutoff (30 Nov 22), 151 pts received ≥1 dose of H3B-6545 during ph1 or ph2. Pts had a median (m [range]) of 2 (1-7) prior endocrine- and 1 (1-6) non-endocrine–containing therapies; 90.1% of pts received prior CDK4/6 inhibitors. During ph1, DLTs of grade (G) 3 rash (n=1) and G 3 fatigue (n=1) were observed at 600 mg; thus, 450 mg was determined to be the MTD/RP2D. In the full analysis set (N=151), 100% and 50.3% of pts had any grade and G ≥3 treatment-emergent adverse events (TEAEs), respectively. TEAEs leading to drug interruption, dose reduction, and withdrawal occurred in 38.4%, 20.5%, and 8.6% of pts, respectively. Nausea (45.7% [2.0% G ≥3]), sinus bradycardia (44.4% [0% G ≥3]), and diarrhea (41.1% [1.3% G ≥3]) were the most common TEAEs. QT prolongation occurred in 9.9% [3.3% G ≥3] of pts. Among 94 response-evaluable pts treated at 450 mg, ORR was 20.2% (95% CI 12.6–29.8) and clinical benefit rate (CBR) was 41.5% (95% CI 31.4–52.1); mPFS (95% CI) was 5.06 (3.15–7.26) months. Among all pts treated at 450 mg (n=115), mOS (95% CI) was 21.52 (16.56–25.46) months. Plasma concentration of H3B-6545 increased as dose increased. Additional results are shown (Table). Conclusions: H3B-6545 had a low rate of G ≥3 TEAEs and showed clinically meaningful antitumor activity in heavily pretreated female patients with ER+, HER2– BC. Clinical trial information: NCT03250676 . [Table: see text]

Inhibition of lysine acetyltransferase KAT6 in ER+HER2− metastatic breast cancer: a phase 1 trial

Inhibition of histone lysine acetyltransferases (KATs) KAT6A and KAT6B has shown antitumor activity in estrogen receptor-positive (ER+) breast cancer preclinical models. PF-07248144 is a selective catalytic inhibitor of KAT6A and KAT6B. In the present study, we report the safety, pharmacokinetics (PK), pharmacodynamics, efficacy and biomarker results from the first-in-human, phase 1 dose escalation and dose expansion study (n = 107) of PF-07248144 monotherapy and fulvestrant combination in heavily pretreated ER+ human epidermal growth factor receptor-negative (HER2−) metastatic breast cancer (mBC). The primary objectives of assessing the safety and tolerability and determining the recommended dose for expansion of PF-07248144, as monotherapy and in combination with fulvestrant, were met. Secondary endpoints included characterization of PK and evaluation of antitumor activity, including objective response rate (ORR) and progression-free survival (PFS). Common treatment-related adverse events (any grade; grades 3–4) included dysgeusia (83.2%, 0%), neutropenia (59.8%, 35.5%) and anemia (48.6%, 13.1%). Exposure was approximately dose proportional. Antitumor activity was observed as monotherapy. For the PF-07248144–fulvestrant combination (n = 43), the ORR (95% confidence interval (CI)) was 30.2% (95% CI = 17.2–46.1%) and the median PFS was 10.7 (5.3–not evaluable) months. PF-07248144 demonstrated a tolerable safety profile and durable antitumor activity in heavily pretreated ER+HER2− mBC. These findings establish KAT6A and KAT6B as druggable cancer targets, provide clinical proof of concept and reveal a potential avenue to treat mBC. clinicaltrial.gov registration: NCT04606446.

The effect of HER2-targeted inhibitors as second-line or later-line regimens in the treatment of HER2-positive advanced colorectal cancer: A systematic review and meta-analysis.

e15542 Background: To systematically evaluate and meta-analyze the efficacy and safety of Human Epidermal Growth Factor Receptor-2 Inhibitor (HER2 Inhibitor) as a second-line or later-line antitumor regimen in the treatment of HER2-positive advanced colorectal cancer and provides a new method to treat metastatic colorectal cancer who failed with first-line treatment. Methods: Literature focusing on the use of HER2-targeted inhibitors in the treatment of HER2-positive mCRC was downloaded from Pubmed, Web of Science, EMBASE and Google Scholar databases from January 1, 2019 to October 31, 2022, and the final included articles were determined by screening and relevant data were extracted, including Objective Response Rate (ORR), disease control rate (DCR), Progression-Free-Survival (PFS), Overall Survival (OS), and Serious Adverse Events (SAEs) (Grade 3/4 adverse events). Binary variables were compared using 95% confidence intervals (CI) and odds ratios (OR); for continuous variables, heterogeneity was checked using Cochran's Q Test (p values and I²) and Weighted mean difference (WMD) and 95% CI. P < 0.05 or I² > 50% denote statistical significance, and results were combined using a random-effects model. The efficacy and safety of adding HER2-targeted inhibitors in treating HER2-positive mCRC were further discussed using the above methods. Results: The systematic review and meta-analysis included 17 studies with a total of 267 patients, with an overall DCR of 57% (95% CI: 43%-70%), an ORR of 29% (95% CI: 21%-37%), a median OS of 13.11 months (95% CI: 10.57-15.64), a median PFS of 4.40 months (95% CI: 3.64-5.15), and SAEs of 20% (95% CI: 0.11-0.29). The efficacy of the second-line and later-line treatment was significantly better than that of the well-known EPIC study, ML18147 study, CONCUR study and FRESCO-2 study. Conclusions: Systematic review and meta-analysis show that HER2-targeted inhibitors as second-line or later-line regimens demonstrate ideal antitumor efficacy and safety in HER2-positive mCRC, which is better than the standard regimen without anti-HER2 therapy. Specifically, the new ADC drug (A antibody-drug Conjugate, ADC) should be able to improve the treatment effect of these patients more effectively. Therefore, HER2-targeted inhibitors can effectively improve the efficacy of second-line and later-line therapy for HER2-positive mCRC. Furthermore, it is still worth exploring its therapeutic effects application as first-line therapy, which is expected to offer new strategies for the clinical diagnosis and treatment of HER2-positive advanced colorectal cancer.

The efficacy and safety of trastuzumab biosimilar HLX02 compared with reference trastuzumab plus pertuzumab in combination with chemotherapy as the first-line treatment for HER2 positive metastatic breast cancer: A real-world study in China.

e13016 Background: Dual-targeted anti-HER2 therapy with trastuzumab (H) and pertuzumab (P) significantly improves outcomes in HER2-positive breast cancer and has become the first-line standard treatment for patients with advanced HER2-positive breast cancer in China in 2019 based on the results of the CLEOPATRA and PUFFIN study. HLX02 (Zercepac) was the first trastuzumab biosimilar manufactured in China. Here, we present the first real-world comparison of HLX02 versus reference trastuzumab (RTZ) and pertuzumab with chemotherapy as the first-line treatment for HER2-positive metastatic China.Between January 2019 and August 2023, 121 patients with HER2-positive MBC patients were enrolled at Beijing Cancer Hospital in China. These patients received HLX02 or RTZ in combination with pertuzumab and various chemotherapies as first-line treatment. We retrospectively analyzed survival outcomes, efficacy, and adverse events. Methods: Between January 2019 and August 2023, 121 patients with HER2-positive MBC patients were enrolled at Beijing Cancer Hospital in China. These patients received HLX02 or RTZ in combination with pertuzumab and various chemotherapies as first-line treatment. We retrospectively analyzed survival outcomes, efficacy, and adverse events. Results: Both groups, 68 received RTZ and 53 received HLX02, showed similar characteristics of age, disease status (de novo or recurrent), metastatic sites (visceral or non-visceral), and treatment history. A total of 118 (97.5%) received trastuzumab plus pertuzumab combined with chemotherapy as the first-line palliative therapy, with a median number of 6 cycles in each group. Taxanes were the most commonly used chemotherapy regimen in both groups (91.2 vs. 92.5%), including nab-paclitaxel (44.1 vs. 45.3%), docetaxel (41.2 vs. 17.0%), paclitaxel (5.9 vs. 30.2%). With a median follow-up of 15.0 months (range 1.0 - 58.0), the results showed no significant difference in PFS between the RTZ and HLX02 arms (median PFS: 22.0 vs. 19.0 months, p=0.900). Additionally, the efficacy outcomes, including objective response rate (ORR), disease control rate (DCR), and safety profiles did not show significant differences between the two groups. Among 121 patients, 20 patients (16.5%) experienced CNS progression. For these patients, the median time from the first-line therapy to the CNS progression was 15.0 months (95% CI 12.8 - 17.2). Conclusions: The real-world data suggest similar efficacy and safety of HLX02 and RTZ plus pertuzumab with different chemotherapy regimens as the first-line treatment for patients with HER2-positive advanced breast cancer patients in China. Overall, the PFS was consistent with the CLEOPATRA trial in both groups, and there was no new safety signal.

First-in-class PD-1/IL-2 bispecific antibody fusion protein IBI363 in patients with other solid tumors: Safety and efficacy results from a phase I study.

e14593 Background: IBI363 is a first-in-class PD-1/IL-2α-bias bispecific antibody fusion protein which could block PD-1 checkpoint and rejuvenate exhausted tumor-specific T cells by cis-activating α-bias IL-2. It was well tolerated and showed encouraging efficacy in patients (pts) with advanced melanoma, non-small cell lung cancer and colorectal cancer. Herein, we report a phase I study of IBI363 in patients (pts) with other solid tumors. Methods: Eligible pts with advanced biliary tract cancer (BTC), head and neck squamous cell carcinoma (HNSCC), cervical cancer (CC) and ovarian cancer (OC) who failed or intolerant to standard therapy were enrolled. IBI363 was intravenously administered at different dose levels ranging from 600 to 1500 μg/kg QW/Q2W/Q3W. Primary objective of the study was safety. Secondary objective was efficacy assessed by investigator per RECIST v1.1 including objective response rate (ORR) and disease control rate (DCR). Results: As of January 26, 2024, 24 pts were enrolled including 13 pts with BTC, 3 pts with HNSCC, 4 pts with CC and 4 pts with OC. In BTC, 6 (46.2%) pts received IBI363 treatment for more than 3 months and the maximum treatment duration was 7 months. In HNSCC, CC and OC, the maximum treatment duration was 4.6, 6.2 and 6.5 months respectively. Pts with at least 1 tumor assessment were included in efficacy evaluable set (n = 18). The overall ORR was 22.2% and DCR was 77.8%. In 11 evaluable pts with BTC, best overall response (BOR) was confirmed partial response (cPR) in 1 pt (600 μg/kg Q2W, immunotherapy (IO)-failed), stable disease (SD) in 9 pts (including 6 pts with tumor regression) and progressive disease (PD) in 1 pt. ORR was 9.1% and DCR was 90.9%. In 2 evaluable pts with HNSCC, 1 pt had cPR (600 μg/kg Q2W, IO-naïve, PD-L1 expression negative) and 1 pt had PD. In 3 evaluable pts with CC, 1 pt had cPR (1000 μg/kg Q2W, IO-failed), 1 pt had SD and 1 pt had PD. In 2 evaluable pts with OC, 1 pt had cPR (1000 μg/kg Q2W, platinum-resistant) and 1 pt had PD. All cPR pts had previous 1-2 lines of treatments and had tumor regression ranging from 45% to 87%. Durable tumor responses were observed with cPR remained at week 30 in BTC and remained at week 24 in HNSCC, CC and OC. In 4 pts with cPR, 3 pts still on treatment and 1 pt with HNSCC received curative resection. No new safety signals of IBI363 were observed. More updated data on safety and efficacy will be presented at the meeting. Conclusions: IBI363 showed promising and durable efficacy in pts with various solid tumors including refractory tumors such as BTC and IO or platinum-resistant tumors such as CC and OC. Further clinical investigations on these tumors using IBI363 alone or in combination with other treatments are ongoing. Clinical trial information: NCT05460767 .

Response to first-line therapies in metastatic lung adenocarcinoma with low PD-L1 expression: A multi-center retrospective study.

e20574 Background: For metastatic lung adenocarcinoma with low PD-L1 expression (tumor proportion score:1-49%), chemotherapy in combination with immune checkpoint inhibitors (IC), with bevacizumab (BC), or with both (IBC) have been established as standard first-line options. However, the optimal scheme is still undetermined. Methods: This retrospective study enrolled 125 metastatic lung adenocarcinoma patients with low PD-L1 expression from four cancer centers. All the patients received IC, BC, or IBC as the first-line therapies. Propensity score matching (PSM) with a ratio of 1:1:1 was used to balance the inter-group clinical characteristics. Efficacy, including objective response rate (ORR), disease control rate (DCR), progression-free survival (PFS) and overall survival (OS), as well as safety were evaluated. Results: 35 of the 125 patients received IBC, 37 received BC, and 53 received IC. After PSM, a total of 35 pairs of patients were enrolled in the analysis. Patients receiving IBC (ORR: 57.1%, DCR:100%) or IC (ORR: 57.1%, DCR: 91.4%) obtained superior ORR and DCR in relative to those receiving BC (ORR: 45.7%, DCR: 82.9%). However, only IBC (median PFS: 20.47m; median OS: not research) rather than IC (median PFS: 10.0m; median OS: 21.36m) treatment generated significantly prolonged PFS and OS compared with BC (median PFS: 9.43m, P = 0.007; median OS: 23.2m, P = 0.048). We further analyzed the survival benefit based on different clinical and molecular features. We found patients with female gender had more significant OS benefit from IBC treatment over IC or BC treatment. In addition, non-smokers benefit more from IBC compared with IC. The occurrence of adverse events (AEs) was more frequent in IBC (74.3%) and IC (85.7%) group in relative to BC group (42.8%). Meanwhile, ≥ grade 3 AEs (22.9%) was markedly higher in IBC group compared with that in BC group (5.7%). However, leukopenia and neutropenia represent the most common ≥ grade 3 AEs, which are easy to be clinically managed. Conclusions: For metastatic lung adenocarcinoma patients with low PD-L1 expression, IBC is the preferred first-line therapy in terms of survival. However, the AEs should be carefully concerned.

Correlation between imatinib trough concentration and efficacy in patients with advanced GIST with different genotypes.

e23515 Background: Imatinib (IM) has significantly enhanced the prognosis of patients (pts) with advanced gastrointestinal stromal tumors (GISTs). The clinical outcomes may correlate with IM exposure. However, the efficacy threshold, particularly based on different primary KIT mutant, remains undefined. This study aimed to establish the efficacy threshold of IM plasma trough concentration (Cmin) at steady-state in Chinese pts with advanced GIST, additionally to define subgroup thresholds based on various primary KIT mutations. Methods: This was a single-center, prospective, observational cohort study. Pts with histologically confirmed recurrent/metastatic GIST who received regular IM treatment and had undergone at least two measurements of steady-state IM Cmin were enrolled from Jul 2017 to Jun 2022. Clinical outcomes including objective response rate (ORR), survival, and IM Cmin were assessed. Results: A total of 168 pts with a median age of 52y were enrolled. The primary lesion locations comprised stomach, small intestine, rectum and others. Metastatic lesions were found in the liver, peritoneum, both liver and peritoneum and others. Median sum of longest diameter of target lesions was 10.7cm. Of 168 pts, 117 (69.6%) harbored KIT 11, 27 (16.1%) harbored KIT 9, 5 (3.0%) harbored PDGFRA, and 9 (5.4%) were KIT/PDGFRA wild type. During IM response period, 104 pts combined with surgical treatment (surgery or interventional therapy). After a median follow-up duration was 50.6m (range, 16.3–189.8), 72 pts had disease progression and 20 died. Estimated median progression-free survival (mPFS) for all patients was 79.4m (95%CI 55.7–103.1). The median overall survival was not reached. A Cmin threshold of ≥738ng/ml defined by log-rank test was associated with longer PFS for the whole population (P = 0.002) irrespective of other clinical characteristics. Pts with an IM Cmin below 738ng/ml exhibited a shorter mPFS (25.3m, 95%CI 41.9–97.1) compared to those surpassing this threshold (96.7m, 95%CI 65.8–127.6). The ORR for the whole population was 73.0% (CR 2.2%, PR 70.8%), with no significant difference observed between pts with IM Cmin below and above 738ng/ml. For pts with KIT 11 and KIT 9 mutations, the efficacy thresholds for IM Cmin were ≥680ng/ml and ≥1877ng/ml, respectively. Multivariate Cox regression analysis revealed that IM Cmin ≥738ng/ml, primary gastric origin, liver-only metastasis, sum of target lesions diameter ≤5cm, KIT 11 mutation, and combined with surgical treatment were favorable prognostic factors. Conclusions: IM exposure significantly correlates with clinical benefits in advanced GISTs, with an IM Cmin above 738ng/ml associated with a longer PFS in Chinese population. Considering different primary KIT mutant, a threshold of 680 ng/ml could be considered for efficacy in KIT 11 mutations, while a higher Cmin of 1877 ng/ml was necessary for KIT 9 mutation.

Stereotactic body radiotherapy (SBRT) combined with transcatheter arterial chemoembolization (TACE) and tyrosine kinase inhibitors (TKIs) versus TACE and TKIs alone for unresectable hepatocellular carcinoma (uHCC) with portal vein tumor thrombus (PVTT): A randomized controlled trial.

4102 Background: TKIs-based systemic therapy is a primary treatment option for uHCC. Clinical studies have established the effectiveness and safety of radiotherapy (RT) in patients with PVTT, who typically have a poor prognosis. Previous research has shown that combining TACE and RT can extend survival in HCC patients with PVTT compared to sorafenib treatment. This study aimed to explore the efficacy and safety of combined local therapy (TACE plus SBRT) and TKIs in HCC patients with PVTT. Methods: This single-center, randomized controlled study enrolled patients aged ≥18 years with HCC and PVTT. Additional eligible criteria included ECOG PS 0-1, Child-Pugh score ≤B7, no extrahepatic metastasis on CT scan, and normal liver volume ≥700cc. Patients were randomly assigned to either the SBRT+TACE+TKIs group (Group A) or the TACE+TKIs group (Group B). SBRT was administered at 35-45 Gy in 5 fractions, 3 fractions per week. TKIs (sorafenib 0.4g bid; donafenib 0.2g bid; or lenvatinib 8mg/12mg qd, depending on body weight) were paused during the perioperative period of TACE (up to 4 times). The primary endpoint was the 6-month progression-free survival (PFS) rate, with secondary endpoints including objective response rate (ORR), overall survival (OS), disease control rate (DCR) and treatment-related adverse events (TRAEs). Treatment response was evaluated using mRECIST. Results: A total of 90 patients with uHCC were enrolled from June 2019 to October 2023 in this trial, with baseline characteristics presented in the Table. As of January 5th 2024, the median follow-up time was 14.5 months [IQR, 2.43-55]. The 6-month PFS rate was significantly higher in Group A (78%) compared to Group B (36%, P=0.0245). Group A also showed prolonged median PFS (9.75 vs. 4.89 months, HR=1.703 [95%CI, 1.045-2.777], P=0.0245) and OS (17.93 vs. 9.61 months, HR=1.869 [95%CI, 1.059-3.266], P=0.017). Improved ORR was observed in the SBRT group (74.4% vs. 40.5%, P=0.0015). DCR was 81.4% in Group A and 66.7% in Group B ( P=0.1211). The most common grade 3/4 TRAEs were hypertension (Group A: 17.8%, Group B: 13.3%, P=0.5608), ALT elevation (Group A: 26.7%, Group B: 22.2%, P=0.6237), and AST elevation (Group A: 22.2%, Group B: 15.6%, P=0.4191). There was one treatment-related death in Group B due to liver failure. Conclusions: In uHCC patients with PVTT, the combination of SBRT and TACE-TKIs showed significant survival benefit without the identification of any severe safety concerns. Clinical trial information: ChiCTR1900025300. [Table: see text]

Exposure-response analyses for optimal therapeutic dose selection of ABBV-383 in patients with relapsed/refractory multiple myeloma (RRMM).

7541 Background: ABBV-383 is a fully human, B-cell maturation antigen (BCMA) × CD3 T-cell–engaging IgG4 bispecific with an effector-silenced Fc region, 2 high-affinity BCMA- and a low-affinity CD3-binding domains. ABBV-383 monotherapy has shown promising activity in patients (pts) with RRMM (Blood 2023;142[suppl 1]:3378). Here, exposure-response (ER) analyses of efficacy and safety endpoints supporting the optimal therapeutic ABBV-383 dose selection are reported in alignment with US FDA’s Project Optimus. Methods: Efficacy (n=218) and safety (n=220) data from the phase 1 study (NCT03933735) escalation cohorts of 0.025 - 120 mg Q3W and expansion cohorts of 20, 40, 60 mg Q3W and 60 mg Q4W including objective response rate (ORR), very good partial response or better (≥VGPR), stringent complete response (sCR)/CR, adverse events (≥G3 and serious), infections (≥G3, overall and serious), cytokine release syndrome (CRS; any-grade, G1, G2, and ≥G2) were modeled. Total(unbound + bound to soluble BCMA) and free (unbound + partially bound to soluble BCMA) Cycle 1 AUCinf, Cmax, and Ctrough and population pharmacokinetic model-derived up to the time of event Cavg and avgCtrough metrics were utilized in the ER analyses (logistic regression; R Version 4.2.2). Relevant pt-specific covariates were tested. Dexamethasone premedication (36 vs 10 mg) was included in CRS models. The ER relationships were utilized to predict the probabilities of efficacy and safety endpoints for relevant doses and thereby, support justification of the optimal therapeutic dose selection. Results: Based on overall assessment, ORR, ≥VGPR, sCR/CR and ≥G3 neutropenia strongly correlated with free Cavg; CRS endpoints (any-grade CRS and G1 only CRS) strongly correlated with Cycle 1 total Cmax (p <0.05). No other endpoints had ER relationships (p >0.05). Only MM type (IgG vs Others) was selected in ≥VGPR and sCR/CR models. ER relationships suggested high response rates of >63% ORR, >53% ≥VGPR, and ≥30% sCR/CR for 40, 60 mg Q3W and 60 mg Q4W. Predictions demonstrated that 20 mg Q3W (<39% ORR and ≥VGPR; <13% sCR/CR) and untested 40 mg Q4W (<60% ORR, <45% ≥VGPR and <23% sCR/CR) provide suboptimal efficacy. The 60 mg Q4W with 36 mg dexamethasone in Cycle1 (limited follow-up and data) was predicted to have ~30% sCR/CR and 31% ≥G3 neutropenia (≈ 40 mg Q3W) and substantially lower any-grade CRS events compared with 40 and 60 mg doses with 10 mg dexamethasone in Cycle 1. Conclusions: While ER analyses indicated promising efficacy and acceptable safety profiles for 40, 60 mg Q3W, and 60 mg Q4W, they support 60 mg Q4W as the optimal ABBV-383 therapeutic dose due to its predicted better therapeutic benefit/risk profile (high response rates, improved/equivalent ≥G3 neutropenia, and lower CRS events) and extended dosing interval. ABBV-383 at 60 mg Q4W will be investigated in the registrational phase 3 trial (NCT06158841) in RRMM.

Abstract PO4-04-01: Antitumor activity and safety of sacibertinib (Hemay022) in combination with endocrine therapy in patients with ER and HER2 both positive metastatic breast cancer: A phase Ib study

Abstract Abstract PURPOSE Sacibertinib (Hemay022) is a novel irreversible tyrosine kinase inhibitor (TKI) blocking epidermal growth factor receptor and human epidermal growth factor receptor 2 (HER2). This study aimed to explore the safety and efficacy of sacibertinib plus endocrine therapy in patients with estrogen receptor-positive ( PATIENTS AND METHODS Using a phase 1b 3+3 dose escalation and expansion study design, patients with ER+/HER2+ MBC were treated with sacibertinib (200mg-500mg daily) plus endocrine therapy including exemestane, letrozole, fulvestrant. The safety, pharmacokinetic and clinical efficacy, including objective response rate (ORR), clinical benefit rate (CBR), disease control rate (DCR) and progression-free survival (PFS) were assessed. RESULTS A total of 55 ER+/HER2+ MBC patients pretreated with chemotherapy and anti-HER2 therapy were enrolled in the study between March, 2018 and July, 2021. The incidence of ORR ranged from 17.6% to 42.9%, DCR ranged from 63.0% to 86.8%, CBR ranged from 42.3% to 69.7%, and the overall median PFS was 9.0 (95% CI, 5.5 ~ 11.00) months. In the 400 mg Sacibertinib plus exemestane cohort (N = 18), ORR was 38.9% (7/18), DCR was 72.2%(13/18), CBR was 66.7%(12/18), and median PFS was 8.9 months; In the 500 mg Sacibertinib plus exemestane cohort (N = 12), ORR was 25.0%(3/12), DCR was 100.0%(12/12), CBR was 50.0%(6/12), and median PFS was 9.0 months. The ORR, CBR, and DCR were better in the 400 mg and above dose cohorts than in the 200 mg and 300 mg cohorts. The DCR of the 500 mg combined with exemestane cohort was better than that of the other dose cohorts. Sacibertinib plus endocrine therapy was well-tolerated without dose-limiting toxicities. The most frequent grade 3 adverse events included diarrhoea (9.1%), leucopenia(5.5%), neutropenia (3.6%). One (1.8%) had grade 4 hydropericardium. CONCLUSION Sacibertinib plus endocrine therapy had a favorable safety profile and antitumor activity in patients with ER+/HER2+ MBC, 400-500mg daily showed more efficacy, supporting further assessment in randomized studies. This figure showed response of Sacibertinib plus endocrine therapy in ER+/HER2+ metastatic breast cancer. Citation Format: Hui-Ping Li, Qingyuan Zhang, Ruyan Zhang, Yaxin Liu, Xianjun Hu. Antitumor activity and safety of sacibertinib (Hemay022) in combination with endocrine therapy in patients with ER and HER2 both positive metastatic breast cancer: A phase Ib study [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-04-01.

Abstract PO2-27-11: Antitumor efficacy and safety of sacibertinib (Hemay022) in combination with endocrine therapy in patients with ER+ and HER2+ metastatic breast cancer: A phase Ib study

Abstract PURPOSE Sacibertinib (Hemay022) is a novel irreversible tyrosine kinase inhibitor (TKI) blocking epidermal growth factor receptor and human epidermal growth factor receptor 2 (HER2). This study aimed to explore the safety and efficacy of sacibertinib plus endocrine therapy in patients with estrogen receptor-positive (ER+) and HER2-positive (HER2+) >metastatic breast cancer (MBC). PATIENTS AND METHODS Using a phase 1b 3+3 dose escalation and expansion study design, patients with ER+/HER2+ MBC were treated with sacibertinib (200mg-500mg daily) plus endocrine therapy including exemestane, letrozole, fulvestrant . The safety, pharmacokinetic (PK) and clinical efficacy, including objective response rate (ORR), clinical benefit rate (CBR), disease control rate (DCR) and progression-free survival (PFS) were assessed. (Clinical Trials.gov identifier: NCT03308201). RESULTS A total of 55 ER+/HER2+ MBC patients pretreated with chemotherapy and anti-HER2 therapy were enrolled in the study between March, 2018 and July, 2021. Fifty-five patients were included in safety analysis and 51 patients were assessed for efficacy analysis. Sacibertinib plus endocrine therapy was well-tolerated without dose-limiting toxicities. The overall median PFS was 9.0 months [95% confidence interval (95% CI), 5.5 ~ 11.0]. The ORR, CBR, and DCR were better in the 400 mg and 500mg dose cohorts than in the 200 mg and 300 mg cohorts. The DCR of the 500 mg combined with the exemestane cohort was better than that of cohorts of other doses. In the 400 mg sacibertinib plus exemestane cohort (N = 18), ORR was 38.9% (7/18) , DCR was 72.2%(13/18), CBR was 66.7%(12/18), and median PFS was 8.9 months (95%CI, 2.7 ~ 16.4 ) ; In the 500 mg sacibertinib plus exemestane cohort (N = 12), ORR was 25.0% (3/12), DCR was 100%(12/12), CBR was 50.0%(6/12), and median PFS was 9.0 months (95%CI, 2.1~NA. Treatment-emergent AEs (TEAEs) were mostly within grades 1–2. The most frequent grade 3 TEAE was diarrhea (9.1%). One (1.8%) had grade 4 abnormal liver function. CONCLUSIONS Sacibertinib plus endocrine therapy had a favorable safety profile and antitumor activity in patients with ER+/HER2+ MBC, 400 -500mg sacibertinib daily showed more efficacy, supporting further assessment in randomized studies. Summary of efficacy data(EAS) NOTE. NA, not available (because cannot be calculated) Treatment-Emergent Adverse Events Occurring in ≥ 10% of Patients in the Safety Population Abbreviations: ALT, alanine aminotransferase; AST, aspartate aminotransferase; Waterfall plot of best change rate in target-lesion size from baseline Citation Format: Hui-Ping Li, Qingyuan Zhang, Ruyan Zhang, Yaxin Liu, Chang Liu, Xianjun Hu. Antitumor efficacy and safety of sacibertinib (Hemay022) in combination with endocrine therapy in patients with ER+ and HER2+ metastatic breast cancer: A phase Ib study [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-27-11.

Abstract PO4-27-05: A phase I open-label dose escalation trial of FWD1802 as monotherapy and in combination with palbociclib in patients with ER+/HER2- unresectable locally advanced or metastatic breast cancer with or without ESR1 mutations

Abstract Background: Estrogen receptor (ER) signaling sits at center of the tumor biology in ER+/HER2- breast cancers. Current standard of care involves hormone therapy with agents including selective estrogen receptor modulators (SERMs), selective estrogen receptor degraders (SERDs), and aromatase inhibitors (AIs). Unfortunately, most patients eventually develop resistance to these therapies. Mutations in estrogen receptor 1 (ESR1) are partially responsible for the acquired resistance. Mutated estrogen receptors are still sensitive to fulvestrant but with a much less sensitivity. In January 2023, elacestrant received its first approval for the treatment of postmenopausal women or adult men with breast cancer harboring ESR1 mutations in US. However, there is still great unmet medical need for this population. FWD1802 is a third-generation oral SERD for ER-positive breast cancer patients. It binds competitively to ER, with a much higher affinity than that of fulvestrant. Preclinically, FWD1802 alone and in combination with palbociclib exhibits significant anti-tumor activity in the ER+/HER2- models and in ESR1-mutated models in vitro and in vivo. This ongoing phase I study is to assess the safety, tolerability, pharmacokinetics (PK) and clinical activity of FWD1802 as monotherapy and in combination with palbociclib in ER+/HER2- unresectable locally advanced or metastatic breast cancer with or without ESR1 mutations. Methods: This clinical study (CTR20232130) consists of three parts: monotherapy dose escalation (Part A), dose escalation in combination with palbociclib (Part B) and monotherapy dose expansion in ESR1-mutated patients (Part C). A conventional “3+3” design is used for this study. Approximately a total of 129 patients will be enrolled. FWD1802 is administered orally daily. In monotherapy dose escalation study (Part A), at each dose level, a single ascending dose (SAD) is followed by a 28-day continuous multiple ascending dose (MAD) period (defined as 1 cycle). In Part B dose, palbociclib (125 mg daily) is administered on a 28-day treatment cycle with 21-day on treatment and 7-day off treatment, along with the 28-day treatment cycle of FWD1802. The primary objectives include dose limiting toxicity (DLT), maximum tolerated dose (MTD), safety, tolerability, and the recommended phase 2 dose (RP2D) of FWD1802. Secondary objectives include pharmacokinetics characteristics of FWD1802 and its major metabolite as monotherapy and in combination with palbociclib. Preliminary anti-tumor activity including objective response rate (ORR), duration of response (DoR), disease control rate (DCR) and progression-free survival (PFS) will also be evaluated. DLT evaluation will be conducted after the first cycle of multi-dose period, and tumor assessment will be conducted every 8 weeks by investigators according to RECIST version 1.1. Patients with ER+/HER2- unresectable locally advanced or metastatic breast cancer with or without ESR1 mutation are eligible for the enrollment. Enrolled patients should have progressed disease, or failed from previous therapy, or intolerable or inaccessible to standard therapy. In addition, patients with ECOG score ≤1 and with adequate renal, cardiac, hepatic, and hematologic function are eligible for enrollment. The monotherapy dose escalation (Part A) is currently ongoing. The dose selection for Part B and Part C will be based on the data from the ongoing Part A. Clinical trial information: CTR20232130. Research Sponsor: Shenzhen Forward Pharmaceuticals Co., Ltd. (FORWARD PHARMA). Citation Format: Ling Zeng, Jin Liu, Dan Wu, Huiwen Ge, Zirui Bian, Chenggang Zhu. A phase I open-label dose escalation trial of FWD1802 as monotherapy and in combination with palbociclib in patients with ER+/HER2- unresectable locally advanced or metastatic breast cancer with or without ESR1 mutations [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-27-05.