Trial results for pembrolizumab in combination with endocrine therapy and palbociclib for postmenopausal patients with newly diagnosed metastatic Stage IV estrogen receptor positive breast cancer were posted on ClinicalTrials.gov on 2026-02-24. The study, NCT02778685, explored different treatment strategies, with one cohort achieving a response rate (complete or partial response) in 15 participants and another demonstrating a complete response in 5 participants. Median duration of response reached up to 27.6 months in one of the treatment arms.
Background
Pembrolizumab is an immunotherapy that may enhance the body's immune system to target cancer cells. The trial investigated its use alongside endocrine therapies like fulvestrant, which blocks estrogen use by tumor cells, and letrozole, which lowers estrogen, as well as palbociclib. This combination approach targets newly diagnosed metastatic Stage IV estrogen receptor positive breast cancer in postmenopausal patients.
Trial design
The study, NCT02778685, was a Phase 2 trial that enrolled 47 postmenopausal participants with newly diagnosed metastatic Stage IV estrogen receptor positive breast cancer. The trial investigated different combinations and sequences of pembrolizumab with endocrine therapy (letrozole or fulvestrant) and palbociclib. The study included three main cohorts:
- Cohort 1: Participants started with letrozole and palbociclib, with pembrolizumab added after 6 months.
- Cohort 2: Participants received letrozole, palbociclib, and pembrolizumab as upfront therapy from the start.
- Cohort 3: Participants received letrozole, palbociclib, fulvestrant, and pembrolizumab.
The trial aimed to evaluate response rates and adverse events across these treatment strategies.
Key results
The trial reported various outcome measurements across the three cohorts:
- For "Response Rate (Complete Response or Partial Response)":
- Cohort 1 (Letrozole + Palbociclib then Pembrolizumab): 2 participants achieved a response.
- Cohort 2 (Letrozole + Palbociclib + Pembrolizumab upfront): 9 participants achieved a response.
- Cohort 3 (Letrozole, Palbociclib, Fulvestrant, Pembrolizumab): 15 participants achieved a response.
- For "Complete Response Rate":
- Cohort 1: 0 participants achieved a complete response.
- Cohort 2: 5 participants achieved a complete response.
- Cohort 3: 1 participant achieved a complete response.
- For "Duration of Response" (Median):
- Cohort 1: Data was NA.
- Cohort 2: The median duration of response was 27.6 months.
- Cohort 3: The median duration of response was 27.1 months.
- For "Incidence of Adverse Events":
- Cohort 1: 4 participants experienced adverse events.
- Cohort 2: 16 participants experienced adverse events.
- Cohort 3: 23 participants experienced adverse events.
What this means
The results from this Phase 2 trial provide insights into the efficacy of different pembrolizumab combination strategies for postmenopausal patients with newly diagnosed metastatic Stage IV estrogen receptor positive breast cancer. The findings suggest that the specific combination and timing of agents can influence patient outcomes, with Cohort 3 showing the highest overall response rate and Cohort 2 demonstrating the highest complete response rate and a substantial median duration of response. These data contribute to understanding potential treatment approaches for this challenging cancer type.
Source
The information regarding these trial results was obtained from ClinicalTrials.gov, a public database of clinical studies. The results for study NCT02778685, titled "Pembrolizumab, Endocrine Therapy, and Palbociclib in Treating Postmenopausal Patients With Newly Diagnosed Metastatic Stage IV Estrogen Receptor Positive Breast Cancer," were posted on 2026-02-24 on clinicaltrials.gov.