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. About 70% of breast tumors express Estrogen Receptors and/or Progesterone Receptors, and Hormone Receptor (HR)-positive/HER2-negative breast cancer is the most frequently diagnosed molecular subtype. Majority of these patients are diagnosed with early stage disease and are often cured with a combination of surgery, radiotherapy, chemotherapy, and hormone therapy. However approximately 20% of patients will experience local recurrence or distant relapse during the first 10 years of treatment. This may be more relevant for those with high risk disease, among whom the risk of recurrence is even greater during the first 2 years, while on adjuvant endocrine therapy, due to primary endocrine resistance. More than 75% of the early recurrences are seen at distant sites.
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. CDK 4 and 6 phosphorylate RetinoBlastoma protein (RB), and initiate transition from the G1 phase to the S phase of the cell cycle. RetinoBlastoma protein has antiproliferative and tumor-suppressor activity. Phosphorylation of RB protein nullifies its beneficial activities. CDK4 and CDK6 are activated in HR-positive breast cancer, promoting breast cancer cell proliferation. Further, there is evidence to suggest that endocrine resistant breast cancer cell lines depend on CDK4 for cell proliferation. The understanding of the role of CDKs in the cell cycle, has paved the way for the development of CDK inhibitors.
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. VERZENIO® is structurally distinct from other CDK 4 and 6 inhibitors (such as Ribociclib and Palbociclib) and is 14 times more potent against Cyclin D1/CDK 4 and Cyclin D3/CDK 6, in enzymatic assays, but potentially less toxic than earlier pan-CDK inhibitors. At higher doses, only VERZENIO® causes significant cancer cell death, compared with other CDK4/6 inhibitors, suggesting that this drug may be affecting proteins, other than CDK4/6. Additionally, preclinical studies have demonstrated that VERZENIO® may have additional therapeutic benefits for a subset of tumors that are unresponsive to treatment or have grown resistant to other CDK4/6 inhibitors. It has also been shown to cross the blood-brain barrier.
The International monarchE trial, is an open-label, randomized, Phase III study, which included 5637 patients, who were pre- and postmenopausal, with HR-positive, HER2-negative early breast cancer, and with clinical and/or pathologic risk factors that rendered them at high risk for relapse. The goal of monarchE was to evaluate the additional benefit of adding a CDK4/6 inhibitor to endocrine therapy in the adjuvant setting, for patients with HR-positive, HER2-negative, high risk, early breast cancer. The researchers defined high risk as the presence of four or more positive axillary lymph nodes, or 1-3 three positive axillary lymph nodes, with either a tumor size of 5 cm or more, or histologic Grade 3 disease (Cohort 1). A smaller group of patients with 1-3 positive axillary lymph nodes and centrally determined Ki-67 score of 20% or more were enrolled in Cohort 2. Ki-67 score was also determined centrally in Cohort 1 patients, but Ki-67 determination was not required for enrollment in this cohort. Following completion of primary therapy which included both adjuvant and neoadjuvant chemotherapy and radiotherapy, patients were randomly assigned (1:1) to VERZENIO® 150 mg orally twice daily for 2 years plus 5-10 years of physician’s choice of endocrine therapy as clinically indicated (N=2808), or endocrine therapy alone (N=2829). The median patient age was 51 years, about 43% of the patients were premenopausal, and 95% of patients had prior chemotherapy. Approximately 60% of patients had 4 or more positive lymph nodes. The Primary endpoint was Invasive Disease-Free Survival (IDFS) in the Intent to Treat (ITT) population (Cohorts 1 and 2). Secondary end points included IDFS in patients with high Ki-67 score (in the ITT population and in the Cohort 1 population), Distant Relapse-Free Survival (DRFS), Overall Survival (OS), and Safety. The researchers reported updated results from an interim analysis to assess overall survival, as well as Invasive Disease-Free Survival and Distant Relapse-Free Survival, with additional follow-up.
At a median follow-up of 42 months (3.5 years), the median Invasive Disease-Free Survival (IDFS) was not reached in either group, and the IDFS benefit previously reported was sustained. The risk of developing invasive disease was reduced by 33.6% (HR=0.664; nominal P<0.0001). The 4-year IDFS rate was 85.8% for patients treated with VERZENIO® plus endocrine therapy, compared to 79.4% for patients treated with endocrine therapy alone, reflecting an absolute difference of 6.4% (compared to 2.8% at two years). The majority of the IDFS events were distant metastatic disease. Adjuvant VERZENIO® also reduced the risk of developing metastatic disease by 34.1% (HR=0.659; nominal P<0.0001). The 4-year DRFS rate was 88.4% for patients treated with VERZENIO® plus endocrine therapy, compared to 82.5% for patients treated with endocrine therapy alone, an absolute difference of 5.9% (compared to 2.5% at two years). As was noted in the previous analyses, a high Ki-67 score correlated with increased risk of recurrence, but this IDFS and DRFS benefit was seen across all prespecified subgroups, regardless of Ki-67 score. Overall Survival (OS) data were immature at the time of this analyses. However, fewer deaths were observed in the VERZENIO® plus endocrine therapy group, compared to endocrine therapy alone. There were no new safety findings, and overall results were consistent with the safety profile for VERZENIO®.
It was concluded that adjuvant VERZENIO® combined with endocrine therapy continued to demonstrate statistically significant and clinically meaningful improvement in Invasive Disease Free Survival and Distant Relapse Free Survival, among patients with HR-positive, HER2-negative, node-positive, high risk, early breast cancer, regardless of Ki-67 status. These benefits were sustained after patients completed 2 years of adjuvant treatment with VERZENIO®, with an absolute increase at 4 years. The authors added that further follow-up is needed to establish whether Overall Survival can be improved with VERZENIO® plus endocrine therapy in this patient group.
Abemaciclib plus endocrine therapy for hormone receptor-positive, HER2-negative, node-positive, high-risk early breast cancer (monarchE): results from a preplanned interim analysis of a randomised, open-label, phase 3 trial. Johnston SRD, Toi M, O’Shaughnessy J, et al. The Lancet Oncology. Published:December 06, 2022. DOI:https://doi.org/10.1016/S1470-2045(22)00694-5
