SOPHIA primary analysis: A phase 3 (P3) study of margetuximab (M) + chemotherapy (C) versus trastuzumab (T) + C in patients (pts) with HER2+ metastatic (met) breast cancer (MBC) after prior anti-HER2 therapies (Tx)

1000

Background: Pretreated HER2+ MBC lacks a defined standard of care, although T is commonly used. M has similar HER2 binding and antiproliferative effects as T. By contrast, M’s Fc region is engineered to increase affinity for both alleles of the activating Fc receptor (FcR), CD16A, and decrease affinity for the inhibitory FcR, CD32B. The low affinity CD16A-158F allele (~85% of population) has been associated with diminished clinical response to T. In a Phase 1 trial, M demonstrated acceptable safety, anti-tumor activity, and evidence of HER2-specific antibody and T-cell responses. Methods: SOPHIA (NCT02492711), a randomized, open-label P3 trial, enrolled pts with HER2+ MBC after pertuzumab and 1–3 lines of prior Tx for MBC. Pts were randomized 1:1 to M (15 mg/kg IV q3w + C) or T (6 [8 for loading dose] mg/kg IV q3w + C), stratified by met sites (≤2, > 2), lines of Tx for met disease (≤2, > 2), and C choice (standard dose capecitabine, eribulin, gemcitabine, or vinorelbine). Primary endpoints are central blinded PFS and OS, assessed sequentially using the stratified log-rank test. Objective response rate (ORR) was a secondary endpoint. 257 PFS events were required to provide 90% power to show PFS superiority at 2-sided α = 0.05. Results: Intent-to-treat analysis (536 pts: M 266; T 270) occurred after 265 PFS events. M prolonged PFS over T (median 5.8 vs 4.9 mo, hazard ratio [HR], 0.76; 95% CI, 0.59–0.98; P= 0.033). Treatment effects were more pronounced in pts with CD16A genotypes containing a 158F allele (median PFS 6.9 vs 5.1 mo, HR, 0.68; 95% CI, 0.52–0.90; P= 0.005). In 524 pts with baseline measurable disease (M 262; T 262), ORR was higher with M (22%; 95% CI, 17.3-27.7%) vs T (16%; 95% CI 11.8-21.0%). Safety profiles were comparable in 529 pts who received study therapy. Grade ≥3 AEs and serious AEs occurred in 138 (52%) and 39 (15%) vs 128 (48%) and 46 (17%) pts on M vs T, respectively. PFS data cutoff: 10/10/18. Conclusions: In combination with chemotherapy in pretreated HER2+ MBC, M improves PFS over T with comparable safety. CD16A genotyping suggests a differential benefit in patients with a 158F allele. OS data are maturing. Clinical trial information: NCT02492711.

Interim results from the full population of the phase 3b CompLEEment-1 study of ribociclib (RIBO) plus letrozole (LET) in the treatment of HR+/HER2– advanced breast cancer (ABC)

1041

Background: RIBO, an oral, selective inhibitor of CDK4/6 (CDK4/6i), is approved for use in combination with endocrine therapy (ET) in women with hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2–) ABC in multiple countries worldwide. Here we report interim safety and efficacy results from CompLEEment-1, a phase 3b trial evaluating RIBO+LET in an expanded patient (pt) population and the largest CDK4/6i trial in ABC to date. Methods: Pts with HR+, HER2– ABC, ≤1 line of prior chemotherapy (CT), and no prior ET for ABC received RIBO+LET. Treatment regimens and study endpoints have been reported previously (De Laurentiis, et al. ASCO 2018. Poster 1056). Results: Overall, 3,246 pts, who received ≥1 dose of study treatment, were evaluated (cut-off date, August 8, 2018). Median duration of RIBO exposure was 8.1 months (min, 0.0; max, 22.4). Demographic and baseline characteristics indicated a diverse population including men (1.2%), premenopausal women (22.2%), and patients aged ≥70 years (19.5%). Pts were well represented in terms of age, race, and disease history; 5.9% of pts received prior CT for ABC. The only non-hematologic any-cause grade ≥3 AEs ≥5% were increased alanine (7.3%) and aspartate (5.3%) aminotransferase. Treatment-related AEs (any grade) led to discontinuation in 11.4% of pts. Of the 51 (1.6%) on-treatment deaths, 26 were due to study indication and 25 to other reasons. The median time to progression was not estimable (NE) (95% confidence interval [CI], 17.1-NE). Overall response rate was 20.5% (95% CI, 19.1%-21.9%) and clinical benefit rate was 66.1% (95% CI, 64.4%-67.7%). Consistent mean change from baseline in Functional Assessment of Cancer Therapy – Breast Cancer questionnaire scores indicated that pts maintained their quality of life throughout treatment. Conclusions: This interim analysis demonstrates the safety, tolerability, and efficacy of RIBO+LET in a large, diverse cohort of pts with HR+, HER2– ABC who had not previously received ET for ABC. Safety results were consistent with those observed in RIBO pivotal studies and no new safety signals were observed. Clinical trial information: NCT02941926.

Phase III study of taselisib (GDC-0032) + fulvestrant (FULV) v FULV in patients (pts) with estrogen receptor (ER)-positive, PIK3CA-mutant (MUT), locally advanced or metastatic breast cancer (MBC): Primary analysis from SANDPIPER

LBA1006

Background: Taselisib, a potent, selective PI3K inhibitor, has enhanced activity in PIK3CA-MUT BC cell lines and confirmed partial responses in PIK3CA-MUT BC as a single-agent or with FULV. We assessed taselisib + FULV in pts with ER-positive, HER2-negative, PIK3CA-MUT locally advanced or MBC. Methods: SANDPIPER (NCT02340221) is a double-blind, placebo (PBO)-controlled, randomized, phase III study. Postmenopausal pts with disease recurrence or progression during or after an aromatase inhibitor were randomized 2:1 to receive taselisib (4 mg oral, qd) or PBO + FULV (500 mg). Stratification factors were: visceral disease, endocrine sensitivity, and geographic region. Pts with PIK3CA-MUT tumors, assessed by central cobas PIK3CA Mutation Test, were randomized separately from non-MUT tumors. The primary endpoint was investigator-assessed progression-free survival (INV-PFS) in pts with PIK3CA-MUT tumors. Secondary endpoints included objective response rate (ORR), overall survival (OS), clinical benefit rate (CBR), duration of objective response (DoR), PFS by blinded independent central review (BICR-PFS), and safety. Results: 516 pts were randomized in the PIK3CA-MUT intention-to-treat (ITT) population. Efficacy is shown in the Table. Taselisib + FULV significantly improved INV-PFS (hazard ratio [HR] 0.70) as confirmed by BICR-PFS (HR 0.66). OS is immature. The most common grade ≥3 adverse events (AEs; preferred terms) in the taselisib + FULV arm in safety-evaluable pts who received ≥ 1 dose of treatment were diarrhea (12%), hyperglycemia (10%), colitis (3%), and stomatitis (2%). AEs led to more taselisib discontinuations (17% v 2%) and dose reductions (37% v 2%), v PBO. Conclusions: Taselisib + FULV significantly improved INV-PFS, v PBO + FULV, in pts with ER-positive, HER2-negative, PIK3CA-MUT locally advanced or MBC. The safety profile is largely consistent with previous studies. Clinical trial information: NCT02340221. [Table: see text]

SANDPIPER: Phase III study of the PI3-kinase (PI3K) inhibitor taselisib (GDC-0032) plus fulvestrant in patients (pts) with estrogen receptor (ER)-positive, HER2-negative locally advanced or metastatic breast cancer (BC) enriched for pts with PIK3CA-mutant tumors

TPS1119

Background: As one of the most frequent genomic alterations in BC, PIK3CA mutations occur in ~40% of ER-positive, HER2-negative breast tumors. PIK3CA mutations may mediate resistance to endocrine therapies and promote growth and proliferation of tumors in BC. Taselisib is a potent and selective PI3K inhibitor that preferentially degrades mutant versus wild-type PI3Kα via a unique mechanism not seen with alpelisib and pictilisib. In PIK3CA-mutant BC cell lines, taselisib had enhanced activity. Confirmed partial responses were reported in pts with PIK3CA-mutant BC treated with taselisib either as a single agent or in combination with fulvestrant. Methods: SANDPIPER is a double-blind, placebo-controlled, randomized, phase III study, designed to evaluate the efficacy and safety of taselisib plus fulvestrant in pts with ER-positive, HER2-negative, PIK3CA-mutant locally advanced or metastatic BC. Postmenopausal pts will be randomized 2:1 to receive either taselisib (4 mg qd) or placebo in combination with fulvestrant (500 mg intramuscular on Days 1 and 15 of Cycle 1, and on Day 1 of each subsequent 28-day cycle). Pts must have had disease recurrence or progression during or after aromatase inhibitor treatment. Randomization will be stratified by visceral disease, endocrine sensitivity, and geographic region. SANDPIPER enriches for pts with PIK3CA-mutant tumors and a centrally assessed, valid cobas PIK3CA Mutation Test result in tumor tissue is required prior to enrollment; pts with PIK3CA-mutant tumors are randomized separately from those with non-mutant tumors. The primary efficacy endpoint is investigator-assessed progression-free survival in pts with PIK3CA-mutant tumors (estimated by Kaplan–Meier methodology). Other endpoints include overall survival, objective response rate, clinical benefit rate, duration of objective response, safety, pharmacokinetics, and patient-reported outcomes. Enrollment is open for pts with PIK3CA-mutant tumors. Target enrollment is 600 pts and > 300 patients have been enrolled. Clinical trial information: NCT02340221.