Larson, Timothy

PURPOSE Imlunestrant is a next-generation oral selective estrogen receptor (ER) degrader designed to deliver continuous ER target inhibition, including in ESR1- mutant breast cancer. This phase Ia/b trial determined the recommended phase II dose (RP2D), safety, pharmacokinetics, and efficacy of imlunestrant, as monotherapy and in combination with targeted therapy, in ER-positive (ER+) advanced breast cancer (ABC) and endometrial endometrioid cancer. The ER+/human epidermal growth factor receptor 2–negative (HER2–) ABC experience is reported here. METHODS An i3+3 dose-escalation design was used, followed by dose expansions of imlunestrant as monotherapy or in combination with abemaciclib with or without aromatase inhibitor (AI), everolimus, or alpelisib. Imlunestrant was administered orally once daily and with the combination partner per label. RESULTS Overall, 262 patients with ER+/HER2– ABC were treated (phase Ia, n = 74; phase Ib, n = 188). Among patients who received imlunestrant monotherapy (n = 114), no dose-limiting toxicities or discontinuations occurred. At the RP2D (400 mg once daily), patients (n = 51) reported grade 1-2 nausea (39.2%), fatigue (39.2%), and diarrhea (29.4%). Patients at RP2D had received previous cyclin-dependent kinase 4/6 inhibitor (CDK4/6i; 92.2%), fulvestrant (41.2%), and chemotherapy (29.4%) for ABC and achieved a median progression-free survival (mPFS) of 7.2 months (95% CI, 3.7 to 8.3). Among patients who received imlunestrant + abemaciclib (n = 42) and imlunestrant + abemaciclib + AI (n = 43), most (69.4%) were treatment-naïve for ABC; all were CDK4/6i-naïve. Patients treated with imlunestrant + everolimus (n = 42)/alpelisib (n = 21) had received previous CDK4/6i (100%), fulvestrant (34.9%), and chemotherapy (17.5%) for ABC. No new safety signals or interactions with partnered drugs were observed. The mPFS was 19.2 months (95% CI, 13.8 to not available) for imlunestrant + abemaciclib and was not reached for imlunestrant + abemaciclib + AI. The mPFS with imlunestrant + everolimus/alpelisib was 15.9 months (95% CI, 11.3 to 19.1)/9.2 months (95% CI, 3.7 to 11.1). Antitumor activity was evident regardless of ESR1 mutation status. CONCLUSION Imlunestrant, as monotherapy or in combination with targeted therapy, had a manageable safety profile with evidence of preliminary antitumor activity in ER+/HER2– ABC.

Background Standard first-line therapies for metastatic colorectal cancer (mCRC) include fluoropyrimidine-containing regimens with oxaliplatin and/or irinotecan and a biologic agent. Immunotherapy may enhance antitumor activity in combination with standard therapies in patients with mCRC. Here, we present phase 2 results of nivolumab plus standard-of-care therapy (SOC; 5-fluorouracil/leucovorin/oxaliplatin/bevacizumab) versus SOC in the first-line treatment of patients with mCRC (CheckMate 9X8). Methods CheckMate 9X8 was a multicenter, open-label, randomized, phase 2/3 trial. Eligible patients were at least 18 years of age with unresectable mCRC and no prior chemotherapy for metastatic disease. Patients were randomized 2:1 to receive nivolumab 240 mg plus SOC or SOC alone every 2 weeks. The primary endpoint was progression-free survival (PFS) by blinded independent central review (BICR) per Response Evaluation Criteria in Solid Tumors V.1.1. Secondary endpoints included PFS by investigator assessment; objective response rate (ORR), disease control rate, duration of response, and time to response, all by BICR and investigator assessments; overall survival; and safety. Preplanned exploratory biomarker analyses were also performed. Results From February 2018 through April 2019, 310 patients were enrolled, of which 195 patients were randomized to nivolumab plus SOC (n=127) or SOC (n=68). At 21.5-month minimum follow-up, PFS with nivolumab plus SOC versus SOC did not meet the prespecified threshold for statistical significance; median PFS by BICR was 11.9 months in both arms (HR, 0.81 (95% CI, 0.53 to 1.23); p=0.30). Higher PFS rates after 12 months (18 months: 28% vs 9%), higher ORR (60% vs 46%), and durable responses (median 12.9 vs 9.3 months) were observed with nivolumab plus SOC versus SOC. Grade 3–4 treatment-related adverse events were reported in 75% versus 48% of patients; no new safety signals were identified. Conclusions The CheckMate 9X8 trial investigating first-line nivolumab plus SOC versus SOC in patients with mCRC did not meet its primary endpoint of PFS by BICR. Nivolumab plus SOC showed numerically higher PFS rates after 12 months, a higher response rate, and more durable responses compared with SOC alone, with acceptable safety. Further investigation to identify subgroups of patients with mCRC that may benefit from nivolumab plus SOC versus SOC in the first-line setting is warranted. Trial registration number NCT03414983 .

8 Background: Standard 1L therapies for mCRC include a fluoropyrimidine with oxaliplatin and/or irinotecan, and a biologic agent. NIVO may enhance antitumor activity in combination with 1L standard therapies within a subset of patients (pts) with mCRC. CheckMate 9X8 evaluated NIVO + mFOLFOX6/BEV vs mFOLFOX6/BEV in 1L mCRC (NCT03414983). Methods: Adults with previously untreated, unresectable, mCRC were randomized 2:1 to NIVO 240 mg + mFOLFOX6/BEV Q2W (NIVO + standard-of-care [SOC]) or mFOLFOX6/BEV Q2W (SOC). Primary endpoint was progression-free survival (PFS) assessed by blinded independent central review (BICR) per RECIST v1.1. Key secondary endpoints included objective response rate (ORR), disease control rate (DCR), time to response (TTR), duration of response (DOR), overall survival (OS), and safety. Results: 195 pts were randomized to NIVO + SOC (n = 127) or SOC (n = 68). Median (range) follow-up was 23.7 (0–33.2) months (mo; NIVO + SOC) vs 23.2 (0–32.3) mo (SOC). Median (range) duration of therapy was 9.9 (0.1–31.8+) mo (NIVO + SOC) and 7.7 (0.1–26.7+) mo (SOC). The HR (95% CI) for PFS was 0.81 (0.53–1.23; P = 0.30), which did not meet the prespecified threshold for statistical significance (median PFS, 11.9 mo in both arms; Table). PFS rates after 12 mo were higher with NIVO + SOC vs SOC (Table). ORR was 60% (NIVO + SOC) and 46% (SOC; odds ratio 1.72 [95% CI 0.96–3.10]) and median (95% CI) DOR was 12.9 (9.0–13.1) mo (NIVO + SOC) and 9.3 (7.5–11.3) mo (SOC; Table). Rates of grade 3−4 treatment-related adverse events (TRAEs) were higher with NIVO + SOC; however, no new safety signals were identified (Table). Biomarker analyses, including tumor mutational burden and baseline CD8 levels, will be presented. Conclusions: The primary endpoint of PFS was not met; however, NIVO + SOC showed higher PFS rates after 12 mo, a higher response rate, and more durable responses compared with SOC, along with acceptable safety, in 1L mCRC. Clinical trial information: NCT03414983. [Table: see text]