Lasofoxifene versus fulvestrant for ER+/HER2- metastatic breast cancer with an ESR1 mutation: results from the randomized, phase II ELAINE 1 trial.

BACKGROUND: Acquired estrogen receptor alpha (ER/ESR1) mutations commonly cause endocrine resistance in ER+ metastatic breast cancer (mBC). Lasofoxifene, a novel selective ER modulator, stabilizes an antagonist conformation of wild-type and ESR1-mutated ER-ligand binding domains, and has antitumor activity in ESR1-mutated xenografts. PATIENTS AND METHODS: In this open-label, randomized, phase II, multicenter, ELAINE 1 study (NCT03781063), we randomized women with ESR1-mutated, ER+/human epidermal growth factor receptor 2 negative (HER2-) mBC that had progressed on an aromatase inhibitor (AI) plus a cyclin-dependent kinase 4/6 inhibitor (CDK4/6i) to oral lasofoxifene 5 mg daily or IM fulvestrant 500 mg (days 1, 15, and 29, and then every 4 weeks) until disease progression/toxicity. The primary endpoint was progression-free survival (PFS); secondary endpoints were safety/tolerability. RESULTS: A total of 103 patients received lasofoxifene (n = 52) or fulvestrant (n = 51). The most current efficacy analysis showed that lasofoxifene did not significantly prolong median PFS compared with fulvestrant: 24.2 weeks (∼5.6 months) versus 16.2 weeks (∼3.7 months; P = 0.138); hazard ratio 0.699 (95% confidence interval 0.434-1.125). However, PFS and other clinical endpoints numerically favored lasofoxifene: clinical benefit rate (36.5% versus 21.6%; P = 0.117), objective response rate [13.2% (including a complete response in one lasofoxifene-treated patient) versus 2.9%; P = 0.124], and 6-month (53.4% versus 37.9%) and 12-month (30.7% versus 14.1%) PFS rates. Most common treatment-emergent adverse events with lasofoxifene were nausea, fatigue, arthralgia, and hot flushes. One death occurred in the fulvestrant arm. Circulating tumor DNA ESR1 mutant allele fraction (MAF) decreased from baseline to week 8 in 82.9% of evaluable lasofoxifene-treated versus 61.5% of fulvestrant-treated patients. CONCLUSIONS: Lasofoxifene demonstrated encouraging antitumor activity versus fulvestrant and was well tolerated in patients with ESR1-mutated, endocrine-resistant mBC following progression on AI plus CDK4/6i. Consistent with target engagement, lasofoxifene reduced ESR1 MAF, and to a greater extent than fulvestrant. Lasofoxifene may be a promising targeted treatment for patients with ESR1-mutated mBC and warrants further investigation.

Phase II study of buparlisib (BKM120) and trastuzumab in patients with HER2+ locally advanced or metastatic breast cancer resistant to trastuzumab-based therapy.

PURPOSE: A Phase Ib study in patients with trastuzumab-resistant, human epidermal growth factor receptor-2- (HER2)-positive advanced breast cancer defined the recommended Phase II dose of buparlisib as 100 mg/day in combination with 2 mg/kg weekly trastuzumab, and reported preliminary signs of clinical activity. Here we present results from the Phase II portion. METHODS: Patients with trastuzumab-resistant, HER2-positive advanced breast cancer received buparlisib plus trastuzumab. Study endpoints included safety/tolerability and antitumour activity. The study was extended to include a Phase Ib dose-escalation phase, in which patients with progressive brain metastases also received capecitabine. RESULTS: In the Phase II portion, of 50 patients treated with buparlisib and trastuzumab, the most common (≥ 30%) all-grade adverse events (AEs) were diarrhoea (54%), nausea (48%), decreased appetite, increased alanine aminotransferase (36% each), increased aspartate aminotransferase (34%), fatigue, rash (32% each), cough and hyperglycemia (30% each). One (2%) patient achieved complete response and four (8%) patients had confirmed partial responses [PR; including two patients with phosphatidylinositol 3-kinase (PI3 K) pathway-activated tumours]. Overall response rate (ORR) was 10%: the primary endpoint (ORR ≥ 25%) was therefore not met. In the Phase Ib portion, all patients with measurable brain lesions at baseline showed tumour shrinkage to some degree; due to low enrollment, maximum tolerated dose of buparlisib in combination with trastuzumab and capecitabine was not determined. CONCLUSION: Buparlisib plus trastuzumab, as a chemotherapy-free regimen, demonstrated an acceptable safety profile but limited efficacy in patients with heavily pretreated, trastuzumab-resistant HER2-positive breast cancer, and in patients with progressive brain metastases also receiving capecitabine.

Outcomes of high-dose chemotherapy and autologous stem-cell transplantation in stage IIIB inflammatory breast cancer.

PURPOSE: To evaluate the disease-free survival (DFS) and overall survival (OS), prognostic factors, and treatment-related mortality of women with stage IIIB inflammatory breast cancer (IBC) treated with combined modality therapy (CMT) and high-dose chemotherapy (HDCT) with autologous stem-cell transplantation. PATIENTS AND METHODS: Between 1989 and 1997, 47 consecutive patients with stage IIIB IBC were treated with CMT and HDCT and were the subject of this retrospective analysis. Chemotherapy was administered to all patients before and/or after definitive surgery. Neoadjuvant and adjuvant chemotherapy was administered to 33 and 34 patients, respectively, and 20 patients received both. All patients received HDCT with autologous stem-cell transplantation, and 41 patients received locoregional radiation therapy. Tamoxifen was prescribed to patients with estrogen receptor (ER)-positive cancer. RESULTS: The mean duration of follow-up from diagnosis was 30 months (range, 6 to 91 months) and from HDCT was 22 months (range, 0.5 to 82 months). At 30 months, the Kaplan-Meier estimates of DFS and OS from diagnosis were 57.7% and 59.1%, respectively. At 4 years, the Kaplan-Meier estimates of DFS and OS from diagnosis were 51.3% and 51.7%, respectively. In a multivariate analysis, the only factors associated with better survival were favorable response to neoadjuvant chemotherapy (P =.04) and receipt of tamoxifen (P =.06); however, the benefit of tamoxifen was only demonstrated in patients with ER-positive breast cancer. At last follow-up, 28 patients (59. 6%) were alive and disease-free. Seventeen patients (36.2%) developed recurrent breast cancer. Seventeen patients died: 15 from disease recurrence and two (4.2%) from treatment-related mortality due to HDCT. CONCLUSION: In this analysis, the early results of treatment with CMT and HDCT compare favorably with other series of patients with stage IIIB IBC treated with CMT alone. These outcomes must be confirmed with longer follow-up and controlled studies.