The phase 3 NATALEE trial's safety data indicates that ribociclib, when administered at a 400-mg dose, exhibits a favorable safety profile in patients with hormone receptor-positive (HR+) early breast cancer. This finding, presented at the European Society for Medical Oncology (ESMO) Annual Congress, supports the use of ribociclib as an adjuvant therapy, balancing efficacy with manageable side effects.
Safety Profile of Ribociclib in NATALEE Trial
The most frequently observed toxicity associated with ribociclib is neutropenia. All-grade neutropenia was reported in 62% of patients, with grade 3 neutropenia occurring in 42%. Elevations in aspartate aminotransferase (AST) and alanine aminotransferase (ALT) were also noted, with all-grade increases in ALT seen in 19% of patients (6% grade 3) and AST increases in 16% (4% grade 3). Notably, the 400-mg dose used in the NATALEE trial is lower than the 600-mg dose used in metastatic disease, which correlates with slightly lower rates of these toxicities. Adverse event-related discontinuations were required in 19% of patients, with a median time to discontinuation of 4 months, indicating that early monitoring is crucial.
Impact of Dose Reduction on Efficacy
An analysis presented at ESMO provided reassurance that dose reductions of ribociclib do not diminish its efficacy. Patients in the NATALEE trial started at 400 mg and could be reduced to 200 mg. This finding aligns with data from the monarchE trial involving abemaciclib, where dose reductions from 150 mg to 100 mg or even 50 mg maintained efficacy. The NATALEE trial only allowed for one dose reduction, unlike the metastatic setting where two dose reductions are permitted.
Managing Liver-Related Adverse Events
Updated analyses from ESMO showed that discontinuation rates remained stable at 20%, with liver-related toxicities being the most common reason for discontinuation. Approximately 9% of patients experienced grade 3 or higher liver-related adverse events. It was noted that if recovery from liver-related AEs did not occur within 28 days, patients were required to discontinue treatment per trial protocol. However, some clinicians have observed that recovery can sometimes take longer, up to 4 to 6 weeks. Dose reduction was often necessary to facilitate the recovery of liver function tests (LFTs).
Ribociclib vs. Abemaciclib: Treatment Considerations
When choosing between adjuvant ribociclib and abemaciclib, clinicians should consider the safety profiles, patient comorbidities, and individual preferences. Ribociclib is administered for 3 years at a dose of 400 mg, while abemaciclib is given for 2 years. While ribociclib is associated with a higher incidence of neutropenia and potential LFT elevations, abemaciclib is more commonly linked to diarrhea. Venous thromboembolism was observed more frequently in patients taking abemaciclib with tamoxifen. Ultimately, the availability of both drugs provides options for tailoring treatment to individual patient needs and tolerability.
Practical Considerations for CDK4/6 Inhibitors
Abemaciclib is available in 50 mg, 100 mg, and 150 mg tablet strengths, typically starting at 150 mg twice daily. Ribociclib is available in 200-mg tablets, with a starting dose of 400 mg. The NATALEE trial included a pack with letrozole, simplifying administration. While monarchE allows for two dose reductions, NATALEE permits only one. These practical considerations, along with the drugs' distinct side effect profiles, inform treatment decisions in the adjuvant setting for HR+ early breast cancer.
