Adjuvant chemotherapy could benefit early-stage ER/PR positive mucinous breast cancer: A SEER-based analysis.

Purpose: The aim of this study was to explore the value of adjuvant chemotherapy in patients with early-stage ER/PR-positive mucinous carcinoma.

Methods: We identified early-stage ER/PR-positive mucinous carcinoma patients in the Surveillance, Epidemiology, and End Results (SEER) database. We used propensity-score matching (PSM) analysis to eliminate selection bias and differences in baseline characteristics. Univariate and multivariate analyses were performed to identify significant prognostic factors. The primary outcomes were overall survival (OS) and breast cancer-specific survival (BCSS), which were evaluated with the Kaplan-Meier method.

Results: After propensity score matching, 805 pairs were selected. Patients with early-stage ER/PR-positive mucinous adenocarcinoma in the chemotherapy group had a better OS, but not BCSS, than those in the nonchemotherapy group after PSM (OS: p < 0.001; BCSS: p = 0.285). After stratifying by tumor size and lymph node status, adjuvant chemotherapy could significantly improve the OS of early-stage ER/PR-positive patients with tumors larger than 3 cm (p = 0.004) if they had negative lymph nodes (LNs). For patients positive LNs, the OS was significantly different between the chemotherapy group and the non-chemotherapy group when the tumors were larger than 1 cm (T = 1-2.9 cm, p = 0.006; T＞3 cm, p = 0.049, respectively).

Conclusion: Adjuvant chemotherapy maybe improves prognosis in patients with negative LNs and tumors larger than 3 cm, or patients with LNs metastasis and tumors larger than 1 cm. We suggest considering clinical characteristics meanwhile when deciding chemotherapy or not. Randomized controlled trials (RCT) are expected to confirm our results in the future.