A look at current and potential treatment approaches for hormone receptor-positive, HER2-negative early breast cancer

The heterogeneity of hormone receptor (HR)-positive, HER2-negative early breast cancers reinforces the importance of individualized, risk-adapted treatment approaches. Numerous factors contribute to the risk for recurrence, including clinical tumor features, individual biomarkers, and genomic risk. Current standard approaches for patients with HR-positive, HER2-negative, early stage disease focus on endocrine therapy and chemotherapy. The specific treatment regimen and duration of adjuvant therapy should be selected based on accurate risk assessment, tolerability of available therapies, and consideration for patient preferences. For patients with high-risk features, such as highly proliferative tumors, large tumor size, and significant nodal involvement, the risk for recurrence remains clinically significant despite appropriate adjuvant treatment with current standards of care. This has driven investigation into novel treatment approaches, including the addition of cyclin-dependent kinase 4 and 6 inhibitors to adjuvant endocrine therapy. Cyclin-dependent kinase 4 and 6 inhibition has demonstrated significant efficacy in patients with high-risk, HR-positive, HER2-negative, nonmetastatic breast cancer and now offers a new strategy to greatly improve outcomes in this difficult to treat patient population.; LAY SUMMARY: Hormone receptor (HR)-positive, HER2-negative early breast cancers are highly diverse and need to be managed differently for individual patients. The use of adjuvant endocrine therapy and chemotherapy should be driven by a patient's risk for recurrence, preferences, and risk for side effects. Patients with high-risk tumors have a persistently elevated risk for recurrence despite current standards of care. Emerging cyclin-dependent kinase 4 and 6 inhibitors are highly effective when added to endocrine therapy in high-risk, HR-positive early breast cancer and have the potential to improve patient outcomes in this difficult to treat patient population.

Adjuvant CDK4/6 inhibitors combined with endocrine therapy in HR-positive, HER2-negative early breast cancer: A meta-analysis of randomized clinical trials

BACKGROUND

The benefit of adjuvant cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors with endocrine therapy (ET) in hormone receptor-positive, human epidermal growth factor 2 receptor-negative (HR+/HER2-) early breast cancer (EBC) is uncertain. Hence, we performed a meta-analysis to determine the efficacy and safety of adjuvant CDK4/6 inhibitors plus ET and to identify potential preferred subpopulations for this regimen.

METHODS

A literature search was conducted in PubMed, Embase, Cochrane databases up to Jan 15, 2021. Hazard ratios (HRs) for invasive disease-free survival (IDFS) and risk ratios (RRs) for grade 3/4 adverse events (AEs) and treatment discontinuation were extracted. Analysis with predefined subgroup variables was done. Trial sequential analysis (TSA) was performed to assess the conclusiveness of survival outcomes.

RESULTS

Three trials were eligible (N = 12647). Compared with ET, adjuvant CDK4/6 inhibitors with ET prolonged IDFS in patients with HR+/HER2- EBC (HR 0.87, 95% CI 0.76-0.98, p = 0.03, I² = 19%), with positive therapeutic responses observed in patients with N2/N3 nodal status (HR 0.83, 95% CI 0.71-0.97, p = 0.02, I² = 0%). None of the cumulative z-curves crossed the trial monitoring boundaries in TSA, and no reliable conclusion could be drawn. The combination treatment carried a higher risk of grade 3/4 AEs (RR 4.14, 95% CI 3.33-5.15, p < 0.00001) and an increase in treatment discontinuation due to AEs (RR 19.16, 95% CI 9.27-39.61, p < 0.00001).

CONCLUSIONS

Adjuvant CDK4/6 inhibitors with ET might provide survival benefit in HR+/HER2- EBC. A statistically significantly improved IDFS was only observed in N2/N3 subgroup. However, overall evidence favoring the use of this combination regimen was inadequate.