Key Points
• This article sums up the findings from several key trials presented at ESMO 2020. Here’s a look at two similar trials with contradicting results: MonarchE and the PALLAS trial.
• In MonarchE, researcher included 5637 patients with early stage breast cancer. These patients were randomized 1:1 to standard-of-care endocrine therapy (ET) alone or the combination of ET with abemaciclib. They were administered this treatment for 2 years.
• The primary outcome, or estimated 2‑years invasive disease-free survival, at a median follow-up of 15.5 months improved from 88.7% in the control group to 92.2% in the experimental group. In total, 16.6% of participants discontinued abemaciclib secondary to toxicity, with 72.8% of patients still within the 2‑year treatment phase at data cut-off.
• The PALLAS trial, researchers randomized 5760 patients with early stage HR-positive/HER2-negative breast cancer to standard ET plus additional adjuvant therapy with palbociclib or control. Invasive disease-free survival rates were similar in both arms at a median follow-up of 23.7 months. Notably, the researchers included patients at lower recurrence risk in the PALLAS trial, with higher discontinuation rates evidenced versus MonarchE. The early overall discontinuation rate was 42.2%, and the early discontinuation secondary to toxicity was 27.1%. Earlier discontinuation could be due to an earlier start of PALLAS when investigators were less experienced clinically with administering CDK4/6 inhibitors, as well as longer follow-up
• “Contradicting outcomes in the two studies may be explained by the mentioned subtle differences in patient characteristics, the lower discontinuation rate in MonarchE, or drug-specific differences. Updated results of the MonarchE trial are awaited at the (virtual) 2020 San Antonio Breast Cancer Symposium; if a continued benefit—or even a larger separation of the curves—is observed, abemaciclib is expected to become an additional adjuvant treatment option in luminal breast cancer at high recurrence risk,” the authors noted.

Key Points
• This article sums up the findings from several key trials presented at ESMO 2020. Here’s a look at two similar trials with contradicting results: MonarchE and the PALLAS trial.
• In MonarchE, researcher included 5637 patients with early stage breast cancer. These patients were randomized 1:1 to standard-of-care endocrine therapy (ET) alone or the combination of ET with abemaciclib. They were administered this treatment for 2 years.
• The primary outcome, or estimated 2‑years invasive disease-free survival, at a median follow-up of 15.5 months improved from 88.7% in the control group to 92.2% in the experimental group. In total, 16.6% of participants discontinued abemaciclib secondary to toxicity, with 72.8% of patients still within the 2‑year treatment phase at data cut-off.
• The PALLAS trial, researchers randomized 5760 patients with early stage HR-positive/HER2-negative breast cancer to standard ET plus additional adjuvant therapy with palbociclib or control. Invasive disease-free survival rates were similar in both arms at a median follow-up of 23.7 months. Notably, the researchers included patients at lower recurrence risk in the PALLAS trial, with higher discontinuation rates evidenced versus MonarchE. The early overall discontinuation rate was 42.2%, and the early discontinuation secondary to toxicity was 27.1%. Earlier discontinuation could be due to an earlier start of PALLAS when investigators were less experienced clinically with administering CDK4/6 inhibitors, as well as longer follow-up
• “Contradicting outcomes in the two studies may be explained by the mentioned subtle differences in patient characteristics, the lower discontinuation rate in MonarchE, or drug-specific differences. Updated results of the MonarchE trial are awaited at the (virtual) 2020 San Antonio Breast Cancer Symposium; if a continued benefit—or even a larger separation of the curves—is observed, abemaciclib is expected to become an additional adjuvant treatment option in luminal breast cancer at high recurrence risk,” the authors noted.