Evaluating the Effectiveness and Toxicities Associated with Novel Oral Agents Palbociclib and Ribociclib to Understand the Influence of Regimen Changes on Disease Progression

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Palbociclib and ribociclib are novel oral cyclin-dependent kinase (CDK)4/6 inhibitors used for the treatment of hormone receptor (HR)-positive metastatic breast cancer. One of the treatment-associated adverse events that have been commonly reported is neutropenia that often necessitates changes in clinical management, including cycle delays and adjustments in medication regimen dose.

García-Trevijano Cabetas and colleagues investigated the effectiveness and toxicities associated with these drugs and evaluated the influence of regimen changes on disease progression. This observational retrospective study was conducted at La Paz University Hospital, a tertiary hospital located in Madrid, Spain.

The HR-positive metastatic breast cancer patients included in the study received initial treatment with palbociclib or ribociclib in the 1-year period between March 2018 and March 2019. The main outcome measure was progression-free survival (PFS).

To ascertain the incidence and severity of neutropenia, and to assess its clinical management, involving dose adjustments and interruptions of treatment, a safety evaluation was performed. The researchers also assessed correlations between regimen changes and effectiveness.

In the study totaling 61 patients, 33 were treated with palbociclib and 28 were treated with ribociclib. Ribociclib was generally (67.9%) used as first-line therapy, whereas palbociclib primarily (81.8%) was used as second-line therapy in the metastatic setting.

In the palbociclib cohort, the median PFS was slightly more than 1 year (12.76 months) and in ribociclib it was not reached. After 1 year, the PFS rate was 78.6% in the ribociclib cohort and 51.5% in the palbociclib cohort.

Occurring in 82.1% of patients receiving ribociclib and 87.9% of patients receiving palbociclib, neutropenia was the most common adverse event.

More than half of the patients treated with palbociclib (63.6%) and ribociclib (64.3%), required cycle delays. In 42.4% and 53.6% of the patients receiving palbociclib and ribociclib, respectively, dose adjustments were required. Statistically significant differences in 12-month PFS rates were not associated with regimen changes.

The outcomes reached in the phase 3 PALOMA-3 and MONALEESA-2 trials for palbociclib and ribociclib were similar to the results reported in this study; however, they cannot be compared using different treatment settings. Given that neutropenia is the most common adverse event, and the toxicity profile is favorable, regimen changes can be used to easily manage conditions. To confirm the trend of no harmful effect on efficacy of these regimen changes, future studies are warranted.

Source:

García-Trevijano Cabetas M, Lucena Martínez P, Jiménez Nácher I, et al. Real-world experience of palbociclib and ribociclib: novel oral therapy in metastatic breast cancer. Int J Clin Pharm. 2021;43:893-899.

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