BARCELONA – Adding the CDK4/6 inhibitor abemaciclib to fulvestrant significantly improves overall survival in hormone receptor–positive (HR+), human epidermal growth factor receptor 2–negative (HER2–) advanced breast cancer patients who progressed on prior endocrine therapy, according to findings from the phase 3 MONARCH 2 trial.
At a median follow-up of 47.7 months, overall survival – a secondary study endpoint – was 46.7 months in 446 patients randomized to receive abemaciclib and fulvestrant, compared with 37.3 months in 223 patients who received placebo and fulvestrant (hazard ratio, 0.757),, reported at the European Society for Medical Oncology Congress.
The overall survival benefit was consistent across stratification factors, which included site of metastasis (visceral, bone, or other) and resistance to prior endocrine therapy (primary versus secondary), but it was most pronounced in patients with visceral disease (HR, 0.675) and primary resistance to prior endocrine therapy (HR, 0.686), said Dr. Sledge, a professor of medicine at Stanford (Calif.) Medical Center.
Progression-free survival, the primary study endpoint, was 16.4 and 9.3 months at the previously reported 2-year follow-up in the treatment and placebo groups, respectively, and the current analysis showed progression-free survival to be “highly consistent” with those findings (16.9 vs. 9.3 months; HR, 0.563), he said.
“Of note, and of interest for further follow-up, a landmark analysis at 3 years shows that approximately three times as many patients on the abemaciclib arm remained progression free, compared to the control arm,” he added, also noting that time from randomization to postdiscontinuation chemotherapy was prolonged with abemaciclib, compared with placebo (50.2 vs. 22.1 months; HR, 0.625).
“A highly significant result,” he said.
At the 47.7 month follow-up, 17% and 4% of patients in the treatment and placebo groups, respectively, remained on treatment.
An additional exploratory analysis showed that 5.8% of patients receiving abemaciclib crossed over to another CDK4/6 inhibitor after discontinuation of therapy, compared with 17.0% of those in the placebo group.
“CDK4/6 inhibitors have emerged as standard-of-care treatment for patients with HR+, HER2– breast cancer,” he said, noting that abemaciclib is a selective CDK4/6 inhibitor with continuous, twice-daily oral administration. “It is approved for monotherapy after progression on endocrine therapy and prior chemotherapy in the metastatic setting, and ... in combination with endocrine therapy in the front-line setting and after progression.”
The global, randomized, double-blind MONARCH 2 trial assessed abemaciclib + fulvestrant in women with advanced endocrine therapy–resistant HR+, HER2– advanced breast cancer, including pre- or perimenopausal women with ovarian suppression and postmenopausal women.
Study participants were randomized 2:1 to receive 500 mg of fulvestrant per label instructions plus 150 mg of abemaciclib every 12 hours or placebo.
Treatment-emergent adverse events in MONARCH 2 were consistent with those previously reported in the primary analysis, Dr. Sledge said.
“Continued follow-up of MONARCH 2 is ongoing to further characterize the overall survival benefit and to look at exploratory efficacy and correlative endpoints,” he noted.
Speaking about the findings during a press conference at the meeting, Nadia Harbeck, MD, a professor at Ludwig Maximilians University, Munich, Germany, said they have important practice-changing implications.
“We were always struggling with whether to give these drugs first or second line, and I think now if we consider the first-line survival benefit ... [first-line use] should be standard of care,” she said, referring to CDK4/6 inhibitors and to findings from MONARCH 2 and prior studies of the inhibitors, including the MONALEESA-3 trial presented at the ESMO Congress.
MONALEESA-3 showed similar overall survival results with the CDK4/6 inhibitor ribociclib in postmenopausal women with HR+, HER2– advanced breast cancer.
“The data are highly clinically meaningful; I think they are going to make a huge impact on how we treat breast cancer,” Dr. Harbeck said.
Dr. Sledge has received trial support, research grants, and travel accommodations from Eli Lilly and Company; is a board member for Tessa Therapeutics; and is a consultant for Syndax, Symphogen, and Verseau Therapeutics. Dr. Harbeck disclosed financial relationships with Agendia, Amgen, AstraZeneca, Celgene, Daiichi-Sankyo, Genomic Health, Lilly, MSD, Nanostring, Novartis, Odonate, Pfizer, Roche, Sandoz/Hexal, and Seattle Genetics. She is also director of the West German Study Group and a member of the German AGO Breast Committee.
SOURCE: Sledge G et al., ESMO 2019, .