Full Compliance of Adjuvant Endocrine Therapy Is Associated with Higher Disease-Free Survival in Hormone Receptor-Positive and HER2-Negative Chinese Breast Cancer Patients with First Tumor Recurrence

PURPOSE: To characterize the compliance status of adjuvant endocrine therapy (aET) and its relationship with disease-free survival (DFS) in hormone receptor-positive (HR+) and HER2-negative (HER2−) in Chinese breast cancer (BC) patients with first tumor recurrence. METHODS: All women with primary unilateral stage I – III HR+HER2− BC and first tumor recurrence in 2008 - 2018 at our institution were identified. Full (vs. none/partial) compliance of aET was classified from records. Multivariate Cox regression estimated the hazard ratio (HR), its 95% confidence interval (CI), and p value. DFS. Covariates included age, T stage, N stage, pathology, tumor grade, LVI, chemotherapy, radiotherapy. RESULTS: A total 258 patients had average age 47.4 years at BC diagnosis and median DFS 31.7 months. Patients with ipsilateral (contralateral) region and organ recurrence were 47.7% (19.8%) and 71.9%. Compared to the patients with none/partial compliance of aET, the full compliance patients (54.3% ) had a higher DFS (median 35.0 vs. 25.2 months, p=0.009). Multivariate analysis showed that the full compliance of aET was associated with a lower HR 0.614 (95%CI 0.467 – 0.807, p<0.001) on recurrence. Early discontinuation (67.5%, 56/83) due to the drug side effects was the top reason for partial compliance of aET. CONCLUSIONS: Full compliance of aET was quite low in Chinese HR+HER2− BC patients. However, it was associated with a 38.6% lower risk of first tumor recurrence. To search for effective tools to improve the compliance of aET in this population should be stressed.