Background: Breast cancer is the most prevalent malignancy among women worldwide. Current evidence supports the use of a CDK4/6 inhibitor combined with endocrine therapy as the preferred first-line treatment for hormone receptor-positive and HER2-negative metastatic breast cancer. This study evaluate the efficacy and safety of CDK4/6 inhibitor plus Fulvestrant in hormone receptor-positive, HER2-negative advanced breast cancer in Vietnam.

Methods: This retrospective analysis was conducted on 80 patients with hormone receptor-positive, HER2-negative advanced breast cancer from January 2020 to December 2024 at Vietnam National Cancer Hospital.

Result: Common sites of metastasis included bone (61.3%), lung (36.3%), and liver (33.8%). The objective response rate was 48.8%, and clinical benefit rate was 80.0%. The overall response rate in the first-line treatment was significantly higher than in the subsequent lines (ORR: 64,6% vs 30,5%; p < 0.01). The median progression-free survival (PFS) was 15.9 months. The median PFS was 24.8 months in the palbociclib arm and 15.9 months in the ribociclib arm with no statistically significant difference. COX multivariate analysis revealed that patients with progesterone receptor-positive status had a 59% lower risk of disease progression or death compared with those with PR-negative status. The incidence of grade 3–4 neutropenia occurred in 58.8% of treatment cycles; 41.3% of patients required at least one dose reduction and 2.5% of patients discontinued treatment due to adverse effects.

Conclusion: CDK4/6 inhibitor plus Fulvestrant is a safe and effective regimen for hormone receptor-positive, HER2-negative advanced breast cancer.

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