PURPOSE We evaluated the impact of 21-gene test results on treatment decisions for patients with early-stage breast cancer treated under the public health care system in Brazil, Sistema Único de Saúde. METHODS Eligible patients treated at Hospital Pérola Byington and Santa Casa de Misericórdia de São Paulo in Brazil were required to have the following characteristics: postsurgery with hormone receptor–positive, human epidermal growth factor 2–negative, node-negative and node-positive, and T1/T2 breast cancer and patients with these characteristics were candidates for adjuvant systemic therapy. Treatment recommendations, chemotherapy plus hormonal therapy (CT + HT) or HT alone, were captured before and after 21-gene test results. RESULTS From August 2018 to April 2019, 179 women were enrolled. The mean age was 58 years (29-86 years), 135 (76%) were postmenopausal, and 58 (32%) had node-positive breast cancer. Most patients (61%) had a tumor > 2 cm, including 7% with tumors > 4 cm. Using Recurrence Score (RS) result cut points on the basis of the TAILORx trial, 40 (22%) had RS 0-10, 91 (51%) had RS 11-25, and 48 (27%) had RS 26-100. Before 21-gene testing, 162 of 179 (91%) patients were recommended for CT. After testing, 117 of 179 patients (65%) had changes in CT recommendation: 112 (63%) who were initially recommended CT received HT alone and five (3%) who were initially recommended HT alone received CT + HT. After 21-gene testing, 99% of physicians reported strong confidence in their treatment recommendations. CONCLUSION The change in clinical practice at these public hospitals was greater than expected: 66% of initial treatment recommendations were changed to omit CT with 21-gene test results. Clinicopathologic features did not correlate well with 21-gene test results and did not adequately identify those most likely to benefit from CT.