Clinical features and survival outcomes of small, node negative breast cancer: A multicenter, retrospective study.

Abstract

e12554 Background: Early-stage breast cancer (T1N0M0 BC) generally has a favorable prognosis, but relapse risks persist over time. The role of adjuvant systemic treatments (AST) for tumors ≤10 mm remains debated. Given the limited availability of robust prospective data, retrospective studies play a crucial role in guiding clinical decision-making. Methods: This multicenter retrospective study analyzed 1,733 pathologically confirmed invasive T1N0M0 breast cancer patients treated at two Chinese medical centers between 1998 and 2018. Patients who received neoadjuvant chemotherapy or with unknown estrogen receptor (ER), progesterone receptor (PR), or human epidermal growth factor receptor 2 (HER2) status were excluded. The primary endpoint was disease-free survival (DFS). Secondary endpoints included distant recurrence-free survival (DRFS), breast cancer-specific survival (BCSS), and overall survival (OS). Clinicopathologic features and survival outcomes were assessed using Kaplan–Meier methods, along with univariate, and multivariate Cox regression models across four molecular subtypes defined by ER, PR and HER2 status. Tumor size thresholds for AST effectiveness were identified using maximally selected rank statistics. Results: Among the 1,733 T1N0M0 cases, HR+/HER2- was the most prevalent subtype (56.9%), followed by HR+/HER2+ (12.6%), HR-/HER2+ (10.8%), and triple-negative (19.7%). Molecular subtypes were significantly associated with survival outcomes. HR+/HER2- subtype had the most favorable 10-year DFS rate of 84.0%, while HR-/HER2+ tumors had the lowest (73.4%). Clinical features such as younger age, premenopausal status, and high histological grade were related to worse outcomes. In the multivariate analysis, early-stage patients treated with adjuvant chemotherapy showed significantly improved DFS compared to patients without AST with a hazard ratio of 0.33 (95% CI: 0.24 to 0.45, p < 0.001). The benefit of AST was also identified for DRFS, BCSS and OS. Tumor size thresholds for AST benefit varied across four subtypes. For HR+/HER2- tumors, neither adjuvant chemotherapy nor endocrine therapy had benefit for tumors < 10 mm ( p = and 0.33, respectively). In contrast, adjuvant chemotherapy with trastuzumab significantly improved DFS for HER2+ tumors ≥ 8 mm (HR = 0.37; 95% CI: 0.14 to 0.77, p = 0.018). Triple-negative tumors ≥ 9 mm also had improved DFS with AST (HR = 0.382; 95% CI: 0.21 to 0.74, p = 0.002). Conclusions: Overall, patients with early-stage breast cancer have a good prognosis. Subtype-specific tumor size thresholds offer a promising approach for decision making of AST in T1N0M0 breast cancer. Patients with larger tumor size might benefit from AST, warranting further investigation in prospective studies.