There is a dearth of efficacy and safety data on palbociclib and ribociclib used in routine clinical practice in India. Rath and colleagues conducted an observational, retrospective, single-institution study that included patients with estrogen receptor–positive and/or progesterone receptor–positive and HER2-negative metastatic breast cancers, and patients who received palbociclib or ribociclib with any partner endocrine therapy between January 2016 and June 2019 in any line of treatment. Progression-free survival (PFS), overall survival (OS), and toxicity data were analyzed.
The median age of patients was 57 years, and 79.2% were postmenopausal. Approximately 58.4% of patients received fulvestrant, 78.2% received palbociclib or ribociclib in second- or later-line treatment, and 40.6% received an aromatase inhibitor.
Median PFS and OS were 21.1 months and not reached, respectively, in first-line treatment, with a median follow-up of 21.7 months. In the second- or later-line settings, median PFS and OS were 5.98 months and 20.2 months, respectively, with a median follow-up of 17.2 months.
Grades 3-4 neutropenia and febrile neutropenia were seen in 45.0% and 9.0% of patients in the second- or later-line settings, respectively. In nearly one-third (31.7%) of patients, dose reduction was required.
This study was considered unique based on previously published real-world data studies. The patients were heavily treated, with 80% of patients receiving cyclin-dependent kinase (CDK)4/6 inhibitors in the second or later lines, and 50% of patients in third- or later-line treatment. They had poorer prognostic characteristics, with 87% having visceral disease and 56% having Eastern Cooperative Oncology Group performance status of 2-3. This differed from pivotal trials, and yet treatment was reasonably well-tolerated with only 3% of patients discontinuing CDK4/6 inhibitors as a result of toxicity.
The investigators concluded that when used in routine clinical practice in first or subsequent lines of treatment, ribociclib and palbociclib resulted in toxicity and efficacy outcomes that were similar and in agreement with pivotal trial expectations.
Rath S, Elamarthi P, Parab P, et al. Efficacy and safety of palbociclib and ribociclib in patients with estrogen and/or progesterone receptor positive, HER2 receptor negative metastatic breast cancer in routine clinical practice. PLoS One. 2021;16:e0253722.
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