SUMMARY: Breast cancer is the most common cancer among women in the US and about 1 in 8 women (12%) will develop invasive breast cancer during their lifetime. Approximately 290,560 new cases of breast cancer will be diagnosed in 2022 and about 43,780 individuals will die of the disease, largely due to metastatic recurrence. Breast cancer is a heterogeneous disease and approximately 70% of breast tumors express Estrogen Receptors and/or Progesterone Receptors. The most common subtype of metastatic breast cancer is Hormone Receptor-positive (HR-positive), HER2-negative breast cancer (65% of all metastatic breast tumors), and these patients are often treated with anti-estrogen therapy as first line treatment. Human Epidermal growth factor Receptor 2 (HER2) overexpression is reported in about 15%-20% of primary breast carcinomas and is associated with poor prognosis, and nearly half of HER2-positive breast cancers are also HR-positive. Patients with HER2-positive breast cancers are generally treated with HER2-targeted therapy combined with chemotherapy. Patients with HER2-positive and HR-positive breast cancer are additionally treated with long-term hormone therapy.
Cyclin Dependent Kinases (CDKs) play a very important role to facilitate orderly and controlled progression of the cell cycle. Genetic alterations in these kinases and their regulatory proteins have been implicated in various malignancies. VERZENIO® (Abemaciclib) is an oral, selective inhibitor of CDK4 and CDK6 kinase activity, and prevents the phosphorylation and subsequent inactivation of the Rb tumor suppressor protein, thereby inducing G1 cell cycle arrest and inhibition of cell proliferation. HERCEPTIN® (Trastuzumab) is a humanized monoclonal antibody targeting HER2 oncogene. FASLODEX® (Fulvestrant) is a parenteral, Selective Estrogen Receptor Degrader (SERD) and is approved for the treatment of postmenopausal women with HR-positive metastatic breast cancer.
monarcHER (NCT02675231) is an International, randomized, multicenter, open-label, three-group, Phase 2 trial, conducted to compare the efficacy of Abemaciclib plus Trastuzumab with or without Fulvestrant, with standard-of-care chemotherapy of physician’s choice plus trastuzumab, in women with advanced breast cancer. In this study, 237 patients were enrolled. Eligible patients had Hormone Receptor (HR)-positive, HER2-positive advanced breast cancer, with unresectable, locally advanced, recurrent, or metastatic disease, and had previously received at least two HER2-targeted therapies for advanced disease. Patients were randomly assigned 1:1:1 to Group A (Abemaciclib, Trastuzumab, and Fulvestrant) N=79, Group B (Abemaciclib and Trastuzumab) N=79, or Group C (standard-of-care chemotherapy and trastuzumab) N=79. Treatment consisted of Abemaciclib 150 mg orally twice daily on days 1-21 of a 21-day cycle, Trastuzumab 8 mg/kg IV on cycle 1, day 1, followed by 6 mg/kg IV on day 1 of each subsequent 21-day cycle, and Fulvestrant 500 mg IM on days 1, 15, and 29 and once every 4 weeks thereafter. Standard-of-care chemotherapy was administered as specified by the product label. Patients were stratified by number of previous systemic therapies for advanced breast cancer and measurable versus non-measurable disease. An exploratory biomarker analysis of breast cancer molecular subtypes was conducted by RNA sequencing. The Primary endpoint was investigator-assessed Progression Free Survival (PFS), first testing Group A versus Group C, and if this result was significant, then Group B versus Group C. Secondary end points included Overall Survival (OS), Overall Response Rate, Patient Reported Outcomes, and pharmacokinetics. Safety was assessed in all patients who had received at least one dose of study treatment.
Previous analyses from this trial revealed that after a median follow up of 19.0 months, the Primary endpoint was met, with significantly superior PFS in Group A compared to Group C (8.3 months versus 5.7 months, respectively, HR=0.67; P=0.051), with a reduction in the risk for disease progression or death of 33%. (Lancet Oncol. 2020;21:763–775). The researchers herein reported the results, after a median follow up of 52.9 months.
The median Overall Survival was 31.1 months in Group A, 29.2 months in Group B and 20.7 months in Group C. When Group A was compared with Group C, the triplet regimen with Abemaciclib, Trastuzumab, and Fulvestrant (Group A) induced a statistically significant improvement in Overall Survival, compared with Trastuzumab plus chemotherapy (Group C). There was a numerically improved Overall Survival benefit with Abemaciclib, in combination with HER2-targeted therapy (Trastuzumab) with or without hormonal therapy (Fulvestrant), compared with chemotherapy plus Trastuzumab, and there was a consistent benefit observed with the addition of Abemaciclib across all pre-specified subgroups. Updated Progression Free Survival and safety findings were consistent with the primary analysis. An exploratory biomarker analysis by RNA sequencing suggested that Luminal subtypes were associated with longer Progression Free Survival (8.6 versus 5.4 months, HR=0.54) and Overall Survival (31.7 versus 19.7 months, HR=0.68), compared to non-Luminal subtypes. The most common serious adverse events in Group A were pyrexia, diarrhea, urinary tract infection, and acute kidney injury (3% each); in Group B were diarrhea and pneumonitis (3% each); and in Group C were neutropenia (6%) and pleural effusion (3%).
The authors concluded that based on this final analysis, a triple-agent, chemotherapy-free treatment regimen consisting of Abemaciclib plus Trastuzumab, with or without Fulvestrant, numerically improved Overall Survival in women with Hormone Receptor-positive, HER2-positive, advanced breast cancer, compared to chemotherapy plus Trastuzumab.
Final overall survival (OS) for abemaciclib plus trastuzumab +/- fulvestrant versus trastuzumab plus chemotherapy in patients with HR+, HER2+ advanced breast cancer (monarcHER): A randomized, open-label, phase II trial. Andre F, Nadal JC, Denys H, et al. Annals of Oncology (2022) 33 (suppl_7): S808-S869. 10.1016/annonc/annonc1089. LBA18
