Hamilton, Erika P

PURPOSE The HER2CLIMB-05 study (ClinicalTrials.gov identifier: NCT05132582 ) is investigating the efficacy and safety of adding tucatinib to trastuzumab and pertuzumab as first-line (1L) maintenance therapy in patients with human epidermal growth factor receptor 2–positive (HER2+) metastatic breast cancer (MBC). METHODS Patients with centrally confirmed HER2+ MBC without evidence of progression post induction therapy and no or asymptomatic brain metastases (BM) were enrolled. Patients were randomly assigned 1:1 to tucatinib (300 mg) or placebo twice a day combined with trastuzumab/pertuzumab. The primary end point is investigator-assessed progression-free survival (PFS); secondary end points include overall survival (OS), PFS per blinded independent central review, CNS-PFS, and safety. RESULTS Between March 2022 and July 2024, 654 patients were randomly assigned to tucatinib (n = 326) and placebo (n = 328) arms. All patients were female (median age, 54 years), 69.3% had de novo MBC, 52.6% were hormone receptor–positive, and 12.4% had presence/history of baseline BM. In this primary analysis, PFS was statistically significantly improved with addition of tucatinib versus placebo (hazard ratio, 0.641 [95% CI, 0.514 to 0.799]; P < .0001; median PFS: 24.9 v 16.3 months); a PFS benefit was seen regardless of the presence/absence of BM or hormone receptor status. OS data remain immature. The most common treatment-emergent adverse events (TEAEs) in the tucatinib arm were diarrhea (72.7%), nausea (33.1%), and elevated liver enzymes (ALT: 28.2%; AST: 25.8%), of which 6.1%, 0.9%, 13.5%, and 7.1%, respectively, were grade ≥3. In the tucatinib arm, 13.5% discontinued tucatinib because of TEAEs. CONCLUSION Tucatinib addition to trastuzumab and pertuzumab demonstrated improvement in PFS with no new safety signals identified and may be an option for 1L maintenance therapy in patients with HER2+ MBC.

Abstract Purpose: CD4 T-cell immunity is associated with improved survival in patients with breast cancer. We previously reported a phase I trial evaluating a folate receptor alpha (FRα) vaccine administered with cyclophosphamide (CP), demonstrating excellent safety and immunogenicity. To simplify the vaccine strategy for ease of use, we report here the results of a randomized phase II trial evaluating a lower vaccine dose alongside the original dose, administered with or without CP pretreatment. Patients and Methods: Patients with triple-negative breast cancer who completed all systemic and local therapies were assigned to receive either low-dose (825 μg) or high-dose (2.5 mg) vaccine peptides plus GM-CSF in six 4-week cycles, with or without CP prior to vaccination. Safety was monitored, and immunogenicity was evaluated before and after vaccination. Results: A total of 80 patients were dosed with vaccine, and 58 patients were evaluable for immunogenicity. Vaccination was well tolerated and elicited immunity in 83% of patients. Levels of FRα-specific T cells were high, persistent, and comparable with T-cell levels against tetanus toxoid. No differences in immunity were observed between the two doses. CP pretreatment also did not affect the immune responses. Recurrences occurred in eight evaluable patients and were unrelated to the treatment arm. No patients died during the study because of their disease. Conclusions: The reduced-dose FRα vaccine is as effective as the original dose and does not require CP to generate maximal immunity. These findings may inform the design of trials testing efficacy in triple-negative breast cancer or other cancers.

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.

Clinical trials frequently include multiple end points that mature at different times. The initial report, typically based on the primary end point, may be published when key planned co-primary or secondary analyses are not yet available. Clinical trial updates provide an opportunity to disseminate additional results from studies, published in JCO or elsewhere, for which the primary end point has already been reported. Two years of adjuvant abemaciclib combined with endocrine therapy (ET) resulted in a significant improvement in invasive disease-free survival (IDFS) and distant relapse-free survival (DRFS) that persisted beyond the 2-year treatment period in patients with hormone receptor–positive, human epidermal growth factor receptor 2–negative, node-positive, high-risk early breast cancer (EBC). Here, we report 5-year efficacy results from a prespecified overall survival (OS) interim analysis. In the intent-to-treat population, with a median follow-up of 54 months, the benefit of abemaciclib was sustained with hazard ratios of 0.680 (95% CI, 0.599 to 0.772) for IDFS and 0.675 (95% CI, 0.588 to 0.774) for DRFS. This persistence of abemaciclib benefit translated to continuous separation of the curves with a deepening in 5-year absolute improvement in IDFS and DRFS rates of 7.6% and 6.7%, respectively, compared with rates of 6% and 5.3% at 4 years and 4.8% and 4.1% at 3 years. With fewer deaths in the abemaciclib plus ET arm compared with the ET-alone arm (208 v 234), statistical significance was not reached for OS. No new safety signals were observed. In conclusion, abemaciclib plus ET continued to reduce the risk of developing invasive and distant disease recurrence beyond the completion of treatment. The increasing absolute improvement at 5 years is consistent with a carryover effect and further supports the use of abemaciclib in patients with high-risk EBC.

Abstract Purpose: To identify potential predictors of response and resistance mechanisms in patients with hormone receptor–positive (HR+), HER2-negative (HER2−) advanced breast cancer (ABC) treated with the cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitor abemaciclib ± endocrine therapy (ET), baseline and acquired genomic alterations in circulating tumor DNA (ctDNA) were analyzed and associated with clinical outcomes. Experimental Design: MONARCH 3: postmenopausal women with HR+, HER2− ABC and no prior systemic therapy in the advanced setting were randomly assigned to abemaciclib or placebo plus nonsteroidal aromatase inhibitor (NSAI). nextMONARCH: women with HR+, HER2− metastatic breast cancer that progressed on/after prior ET and chemotherapy were randomly assigned to abemaciclib alone (two doses) or plus tamoxifen. Baseline and end-of-treatment plasma samples from patients in MONARCH 3 and nextMONARCH (monotherapy arms) were analyzed to identify somatic genomic alterations. Association between genomic alterations and median progression-free survival (mPFS) was assessed. Results: Most patients had ≥1 genomic alteration detected in baseline ctDNA. In MONARCH 3, abemaciclib+NSAI was associated with improved mPFS versus placebo+NSAI, regardless of baseline alterations. ESR1 alterations were less frequently acquired in the abemaciclib+NSAI arm than placebo+NSAI. Acquired alterations potentially associated with resistance to abemaciclib ± NSAI included RB1 and MYC. Conclusions: In MONARCH 3, certain baseline ctDNA genomic alterations were prognostic for ET but not predictive of abemaciclib response. Further studies are warranted to assess whether ctDNA alterations acquired during abemaciclib treatment differ from other CDK4/6 inhibitors. Findings are hypothesis generating; further exploration is warranted into mechanisms of resistance to abemaciclib and ET. See related commentary by Wander and Bardia, p. 2008

PURPOSE To evaluate the efficacy and safety of tucatinib and trastuzumab in patients with previously treated human epidermal growth factor receptor 2–positive (HER2+) metastatic biliary tract cancer (mBTC). METHODS SGNTUC-019 (ClinicalTrials.gov identifier: NCT04579380 ) is an open-label phase II basket study evaluating the efficacy and safety of tucatinib and trastuzumab in patients with HER2-altered solid tumors. In the biliary tract cancer cohort, patients had previously treated HER2 overexpressing or amplified (HER2+) tumors (identified with local testing) with no prior HER2-directed therapy. The primary end point was confirmed objective response rate (cORR) per investigator assessment. Patients were treated on a 21-day cycle with tucatinib (300 mg orally twice daily) and trastuzumab (8 mg/kg intravenously followed by 6 mg/kg every 3 weeks). RESULTS Thirty patients were enrolled. As of data cutoff (January 30, 2023), the median duration of follow-up was 10.8 months. The cORR was 46.7% (90% CI, 30.8 to 63.0), with a disease control rate of 76.7% (90% CI, 60.6 to 88.5). The median duration of response and progression-free survival were 6.0 months (90% CI, 5.5 to 6.9) and 5.5 months (90% CI, 3.9 to 8.1), respectively. At data cutoff, 15 patients (50.0%) had died, and the estimated 12-month overall survival rate was 53.6% (90% CI, 36.8 to 67.8). The two most common treatment-emergent adverse events (TEAEs) were pyrexia (43.3%) and diarrhea (40.0%). Grade ≥3 TEAEs were reported in 18 patients (60.0%), with the most common being cholangitis, decreased appetite, and nausea (all 10.0%), which were generally not treatment related. TEAEs led to treatment regimen discontinuation in one patient, and there were no deaths due to TEAEs. CONCLUSION Tucatinib combined with trastuzumab had clinically significant antitumor activity and was well tolerated in patients with previously treated HER2+ mBTC.