Treatment decisions for patients with T1a,bN0M0 breast cancer are challenging. We studied the time trends in use of adjuvant chemotherapy and survival outcomes among these patients.

This was a prospective cohort study within the National Comprehensive Cancer Network Database that included 4,113 women with T1a,bN0M0 breast cancer treated between 2000 and 2009. Tumors were grouped by size (T1a, T1b), biologic subtype defined by hormone receptor (HR) and human epidermal growth factor receptor 2 (HER2) status, and receipt of chemotherapy with or without trastuzumab.

Median follow-up time was 5.5 years. Eight percent of patients with HR-positive/HER2-negative tumors were treated with chemotherapy. Fifty-two percent of those with HER2-positive or HR-negative/HER2-negative breast cancers received chemotherapy, with an increase over the last decade. Survival outcomes diverged by subtype and size, but the 5-year distant relapse-free survival (DRFS) did not exceed 10% in any subgroup. The 5-year DRFS for patients with T1a tumors untreated with chemotherapy ranged from 93% to 98% (n = 49 to 972), and for patients with T1b tumors, it ranged from 90% to 96% (n = 17 to 2,005). Patients with HR-positive/HER2-negative disease had the best DRFS estimates, and patients with HR-negative/HER2-negative tumors had the lowest. In this observational, nonrandomized cohort study, the 5-year DRFS for treated patients with T1a tumors was 100% for all subgroups (n = 12 to 33), and for patients with T1b tumors, it ranged from 94% to 96% (n = 88 to 241).

Women with T1a,b tumors have an excellent prognosis without chemotherapy. Size and tumor subtype may identify patients in whom the rate of recurrence justifies consideration of chemotherapy. These patients represent an optimal group for evaluating less toxic adjuvant regimens to maintain efficacy while minimizing short- and long-term risks.