Tailoring Escalated Adjuvant Chemotherapy for Multifocal and Multicentric Breast Cancer With Low Tumor Burden

The prognostic significance of multifocal and multicentric breast cancer (MMBC) with low tumor burden remains controversial, and adjuvant chemotherapy guidelines for these patients are lacking.

Female patients with cT1-T2 MMBC or unifocal breast cancer (UBC) diagnosed between 2010 and 2020 were identified from the SEER database. Propensity score matching (PSM) balanced baseline characteristics. Survival outcomes were evaluated using Kaplan-Meier and Cox proportional hazards models, with subgroup analyses stratified by tumor size in node-negative MMBC.

After PSM, 9,751 matched pairs of patients with MMBC and UBC were included. Analyses showed MMBC had significantly worse overall survival (OS) and breast cancer-specific survival (BCSS) than UBC (both P < .001). Multivariate Cox regression confirmed chemotherapy improved OS (hazard ratio [HR], 0.583 [95% CI, 0.522 to 0.652]) and BCSS (HR, 0.830 [95% CI, 0.702 to 0.980]) in MMBC. In eligible cases, 1,731 matched pairs with and without chemotherapy were identified. Subgroup analyses showed that in node-negative MMBC, chemotherapy improved OS only when tumors were ≥1 cm (tumor <1 cm: HR, 0.804 [95% CI, 0.506 to 1.275], P = .353; 1-2 cm: HR, 0.577 [95% CI, 0.414 to 0.806], P = .001; ≥2 cm: HR, 0.535 [95% CI, 0.399 to 0.717], P < .001).

MMBC predicts poorer survival than UBC. In node-negative MMBC, chemotherapy confers benefit only when tumor size is ≥1 cm, suggesting multifocality and multicentricity should guide chemotherapy decisions. Prospective studies are warranted to confirm findings and refine guidelines.