|The following article features coverage from the 2019 San Antonio Breast Cancer Symposium. Click here to read more of Cancer Therapy Advisor‘s conference coverage.|
For patients with hormonal receptor (HR)-positive, HER2-negative metastatic breast cancer, endocrine therapy with palbociclib did not offer a progression-free survival (PFS) advantage over capecitabine, according to data from the phase 3 PEARL study. The trials results were presented at the 2019 San Antonio Breast Cancer Symposium (SABCS) in Texas.
The study had 601 patients with HR-positive, HER2-negative metastatic breast cancer that progressed during treatment with aromatase inhibitors. Patients were split between 2 cohorts: Cohort 1 was 296 patients who were randomized to receive either exemestane and palbociclib or capecitabine alone, and cohort 2 was 305 patients who were randomized to receive either fulvestrant and palbociclib or capecitabine alone.
Cohort 2 was added to the study in 2016 when data emerged that ESR1 mutations may lead to resistance to aromatase inhibitors, but not fulvestrant. Among the patients in cohort 2, ESR1 mutations were found in 28.2%.
At a median follow-up of 13.5 months, the median PFS for patients who received fulvestrant and palbociclib was not significantly different from those who received capecitabine (7.5 vs 10 months, respectively; adjusted hazard ratio [HR], 1.09; 95% CI, 0.83-1.44; P =.537).
When evaluated by subtype, still no PFS advantage was seen for patients with luminal or nonluminal tumors who received fulvestrant and palbociclib.
At a median follow-up of 19.0 months for patients without an ESR1 mutation, the median PFS for patients who received endocrine therapy plus palbociclib was not significantly different from those who received capecitabine (8.0 vs 10.6 months, respectively; adjusted HR, 1.08; 95% CI, 0.85-1.36; P =.526). Again, no PFS advantage was seen for patients with luminal or nonluminal tumors who received endocrine therapy and palbociclib.
Patients who received fulvestrant and palbociclib, or exemestane and palbociclib, also had higher rates of grade 3/4 neutropenia than patients who received capecitabine (57.4% and 55.7% vs 5.5%, respectively).
“The combination of palbo plus endocrine therapy of any case was not superior to capecitabine in patients with ESR1 wild-type tumors,” said the study presenter Miguel Martín, Instituto de Investigación Sanitaria Gregorio Marañón.
He added, “On the other hand, therapy with palbociclib plus endocrine therapy was generally better tolerated than capecitabine.”
The treatment discontinuation rate was lower for endocrine therapy plus palbociclib than capecitabine (3.7% vs 12.8%, respectively).
Disclosure: Some of the authors disclosed financial relationships with the pharmaceutical industry. For a full list of disclosures, please refer to the original abstract.
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Martín M, Zielinski C, Ruíz-Borrego M, et al. Results from PEARL study (GEICAM/2013-02_CECOG/BC.1.3.006): A phase 3 trial of Palbociclib (PAL) in combination with endocrine therapy (ET) versus Capecitabine (CAPE) in hormonal receptor (HR)-positive/human epidermal growth factor receptor (HER) 2-negative metastatic breast cancer (MBC) patients (pts) whose disease progressed on aromatase inhibitors (AIs). Oral presentation at: 2019 San Antonio Breast Cancer Symposium; December 10-14, 2019; San Antonio, TX. Abstract GS2-07.