Abstract BACKGROUND The benefit of chemotherapy in very early-stage triple-negative breast cancer (TNBC) remains unclear, as these patients have historically been excluded from clinical trials. Guidelines recommend consideration of chemotherapy for T1b tumors (0.6-1 cm) and is not recommend for T1a tumors (≤0.5 cm). However, treatment utilization is heterogeneous, and the benefit remains poorly defined. We aim to evaluate recent trends in treatment patterns, outcomes, and provider decision-making for patients with stage IA TNBC. METHODS We conducted a single-institution retrospective study from Jan 2016-Jan 2025 of patients with TNBC, pathologic T1a (≤5 mm) or T1b (5-10 mm), and pN0, pN0(i+), or pN1mi disease. Patients were stratified by pT stage and chemotherapy receipt. Kaplan-Meier curves assessed survival; logistic regression identified factors associated with chemotherapy use. RESULTS Among pT1a, 20.6% (n=13) received chemotherapy. Older age was associated with a significantly lower likelihood of chemotherapy use, while BRCA1(+) was associated with a significantly higher likelihood of receiving chemotherapy. Among pT1b, 67.6% (n=94) received chemotherapy. Older age and ECOG 1 (vs 0) were associated with a significantly lower likelihood of receiving chemotherapy; tumor grade III and invasive ductal carcinoma histology were associated with a significantly higher likelihood of chemotherapy. Recurrence and survival estimates are displayed in Table 1. Decision-making documentation was available for 191 (95%) cases. In pT1a, multifocal disease was the most frequently cited factor (33%) when chemotherapy was recommended. In pT1b, high comorbidities (30%), patient preference (20%), favorable histology (20%), and lack of data (20%) were the most cited reasons for recommending surveillance. Lack of high evidence data and departmental group discussions were cited in discussions across all subgroups. CONCLUSION Although 3-year OS and RFS were generally favorable, recurrences occurred in all groups except pT1a patients who received chemotherapy. This cohort represents a very important group of patients for whom oncologists must balance the risk of overtreatment with chemotherapy, while also ensuring high-risk patients receive appropriate care. Qualitative review of documentation revealed that clinical decision-making was often driven by nuanced considerations, including multifocal disease, histologic subtype, patient comorbidities, and patient preference; consistent references to lack of high-level evidence data and discussion at departmental meetings highlight the ambiguity and complexity in these cases. These findings underscore the need for prospective data and validated risk tools to guide chemotherapy decisions in T1a/b TNBC tumors. Citation Format: E. R. Lopez, A. Raghavendra, S. Pasyar, B. Lim, K. Meghan, V. Valero, C. H. Barcenas. Chemotherapy Decision Making and Outcomes in Very Early-Stage Triple Negative Breast Cancer abstract. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS4-07-22.
Lopez et al. (2026) studied this question.