Background: Limited information exists regarding tumor response to palbociclib plus an aromatase inhibitor (AI) versus AI alone in real-world practice.
Objective: To evaluate the real-world tumor response of palbociclib plus letrozole (PAL+LET) versus LET alone as first-line treatment for patients with hormone receptor-positive/human epidermal growth factor receptor 2-negative metastatic breast cancer (HR+/HER2‒ MBC) in routine US clinical practice.
Patients and methods: This retrospective analysis included HR+/HER2‒ MBC patients who initiated PAL+LET or LET as first-line treatment between February 2015 and September 2018 in the Flatiron Health Analytics database. Patients were followed until December 2018. Real-world best tumor response (rwBTR) was determined based on physicians' assessment of radiologic evidence for change in burden of disease.
Results: Of the 1383 eligible patients who initiated PAL+LET or LET as first-line therapy in the Flatiron database, 968 patients had ≥ 1 tumor response assessment (662 received PAL+LET and 306 received LET). The rwBTR rate (complete response+partial response) in the first-line setting was 59.8% in the PAL+LET group and 39.2% in the LET group (odds ratio 2.31 (95% CI 1.75‒3.04), P < 0.0001). After 1:1 propensity-score matching, the rwBTR rate was 58.6% in the PAL+LET group versus 39.1% in the LET group (odds ratio 2.21 (95% CI 1.50‒3.25), P < 0.0001).
Conclusions: This real-world analysis demonstrated that HR+/HER2‒ MBC patients were more likely to respond to PAL+LET compared to LET. These findings further showed the effectiveness of PAL+LET therapy in the real-world setting and support the combination as a standard of care for MBC.
Study registration: Pfizer; NCT04176354; registered November 25, 2019.
Palbociclib (Ibrance®; PAL) is a treatment for advanced or metastatic breast cancer (MBC for short). Metastatic means that the cancer has spread from breast tissue to other areas of the body. PAL is taken with medications known as hormone therapy, such as letrozole (LET), to treat people with a type of MBC called hormone receptor‒positive, human epidermal growth factor receptor 2–negative (HR+/HER2‒). Researchers wanted to understand more about how treatment with PAL+LET affected tumor response (i.e., if the tumor shrinks or disappears) in women with HR+/HER2– MBC. We looked at tumor response to PAL+LET in a real-life setting using anonymous medical record information from a database of about 2.4 million US patients with cancer. This study included 1383 patients with HR+/HER2‒ MBC who started PAL+LET (754 patients) or LET alone (629 patients) as their first MBC treatment from 2015‒2018. Among people who took PAL+LET, 60% people had a tumor response compared with 39% of people who took LET alone. Of the people who took PAL+LET, half of the people lived with their cancer without it getting worse for at least 20 months compared with 15 months for people who took LET alone. These results add to what is known about PAL+LET treatment based on routine clinical practice and clinical trials. Both types of information provide support for PAL+LET treatment as the standard care for women with HR+/HER2‒ MBC. Video Abstract (MP4 90112 kb).
© 2021. The Author(s).