Adjuvant treatments for stage I breast cancers of one centimeter or less.

PURPOSE OF REVIEW: The increasing detection of subcentimetric breast cancers (BC) through widespread implementation of mammographic screening has raised important questions regarding the optimal management of patients with stage I tumors measuring ≤1 cm in the adjuvant setting. Although these tumors exhibit an overall excellent prognosis, outcomes are heterogeneous and influenced by biological factors and patients characteristics. This review summarizes current evidence on adjuvant systemic treatments and discusses emerging approaches to treatment individualization. RECENT FINDINGS: Evidence supporting adjuvant systemic treatments in subcentimetric stage I BC remains limited, as these tumors have been underrepresented in most pivotal clinical trials and current recommendations are partly based on retrospective evidence. In hormone receptor-positive disease, endocrine therapy remains the cornerstone of treatment, while chemotherapy could be considered according to genomic assays, in selected cases. In HER2-positive tumors, trastuzumab-based de-intensified regimens have demonstrated excellent outcomes. In triple-negative BC, chemotherapy appears to provide the greatest benefit in selected higher-risk tumors. SUMMARY: Treatment decisions in subcentimetric stage I BC should incorporate biological characteristics and patient factors beyond tumor size. Ongoing treatment optimization trials, together with integrated risk prediction models and emerging biomarkers, including circulating tumor DNA and tumor-infiltrating lymphocytes, may improve patient selection for treatment modulation strategies aimed at maximizing benefit while minimizing unnecessary toxicity.