Real world outcomes of 2,339 patients with early-stage triple-negative breast cancer (TNBC) treated in British Columbia.

e23274 Background: TNBC represents 15-20% of all breast cancers, and tends to exhibit more aggressive features, more frequent distant metastasis and overall worse prognosis than other breast cancer subtypes. The treatment landscape for early-stage TNBC has changed considerably in the last decade, with new additions to neoadjuvant therapy (NAT) aimed at improving pathologic responses and outcomes. In this study, we assess real world data regarding treatment and outcomes in those with early-stage TNBC. Methods: The BC Cancer Breast Cancer Outcomes Unit database contains prospectively collected data on patients residing in British Columbia and diagnosed with breast cancer since 1989. This retrospective study evaluated patients diagnosed with stage I-III TNBC from 2010 to 2019. During this era, regimens containing anthracyclines and taxanes were routinely used. TNBC was defined as per ASCO-CAP guidelines as ER≤1%, PR≤1% and negative HER 2 (0, 1+ by immunohistochemistry, or 2+ ISH negative). Outcomes of interest included event free survival (EFS), overall survival (OS), and pathologic complete response (pCR). Results: 2,339 patients withstage I-III TNBC were identified with a mean follow up of 6.5 years. OS was 87% (95% CI 85-88%) at 3-years and 79% (95% CI 77-80%) at 5-years. The presenting stage was a significant prognostic factor, with 5-year EFS of 89%, 81% and 51%- and 5-year OS of 90%, 80%, and 53% for stages I, II, and III, respectively. There was an increase in NAT use in 2019 (n = 82/230,35.7%) when compared to 2010 (n = 20/227, 8.8%). The most common neoadjuvant regimens used included anthracycline and taxane chemotherapies (n = 343,81.4%), with only a small number receiving neoadjuvant platinum chemotherapy (n = 52, 12.4%). Pathological complete response (pCR) was achieved in 24.5% (103/421) of patients who received NAT. Patients with pCR had improved 5- year EFS (91% vs. 57%, HR 0.26 [95% CI 0.15-0.45]) and 5-year OS (90% vs. 59%, HR 0.26 [95% CI 0.15-0.45]) compared to those with residual disease. The subgroup that received salvage capecitabine had a poor 3-year EFS at 22% but was enriched for patients with residual nodal disease after NAT (n = 77/130, 59.2%). Conclusions: This real-world study of TNBC in the era prior to routine immunotherapy (IO), highlights the poor prognosis of TNBC, particularly patients with locally advanced disease and those who did not achieve pCR, despite adjuvant capecitabine. This stresses the need for advances in NAT and salvage therapies for TNBC with residual disease at high risk of recurrence. [Table: see text]