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ASCO published a guideline in 2020 on the . Now, an identified clinical trials that studied two specific CDK4/6 inhibitors (abemaciclib and ribociclib) for breast cancer and put forth two recommendations for CDK inhibitors.

For patients with resected tumors that are hormone-receptor positive (HR+) and HER2 negative, abemaciclib 150 mg twice daily for 2 years in conjunction with endocrine therapy is recommended for those with a high risk of recurrence, as defined by 4 or more positive axillary lymph nodes (ALNs) or 1-3 ALNs in combination with either grade 3 disease, a tumor larger than 5 cm, or a Ki-67 index score greater than 20%. This is consistent with the enrollment criteria for the monarchE clinical trial. The with a 54-month median follow-up shows a hazard ratio of 0.680 for the addition of abemaciclib to endocrine therapy, and a 5-year absolute improvement in invasive disease-free survival (IDFS) of 7.6%, with a deepened benefit over time.

For patients with stage II and III breast cancer, ribociclib 400 mg, 3 weeks on and 1 week off, is recommended with endocrine therapy for those who meet the enrollment criteria. This trial included stage II-III HR+, HER2-negative early breast cancer. Patients with stage IIA (T2N0) were enrolled if they had grade 2 disease and a Ki-67 index score greater than or equal to 20% or high genomic risk or grade 3 disease. At a median follow-up of 27.7 months, the addition of adjuvant ribociclib significantly improved IDFS with a hazard ratio of 0.75 and a 3.3% absolute benefit at 3 years.

The ASCO expert panel made the following two qualifying statements: Not all patients who would have met clinical trial eligibility may derive a meaningful clinical benefit from CDK 4/6 inhibitors. Specifically, for most with node-negative disease, the risks may outweigh the benefits, except for the very high-risk node-negative patients, though there are insufficient data to specify which subgroups should and should not be treated. Risks, benefits, cost, and patient preferences must be considered. For patients meeting the criteria for both CDK 4/6 inhibitors, the panel favors abemaciclib, given its longer follow-up, shorter treatment course, deepened benefit over time, and FDA approval. Ribociclib, not yet FDA approved in the adjuvant setting, could be considered for patients with a contraindication or intolerance to abemaciclib.

These two recommendations provide an excellent framework for clinicians considering prescribing CDK4/6 inhibitors, though more research is needed on the survival benefit CDK4/6 inhibitors confer and to what degree their efficacy varies by breast cancer stage.

Ruta Rao, MD, and Rachel Akers, Rush University Medical Center, Chicago.

Read the study here and an interview about it here.