National trends in neoadjuvant systemic therapy utilization in patients with early-stage HER2-positive breast cancer from 2016-2021: The impact of the KATHERINE trial.

purposeNeoadjuvant systemic therapy (NST) for HER2 + breast cancer (HER2 + BC) has historically been used to downstage disease to facilitate surgical de-escalation; however, in 2019, the KATHERINE trial identified a survival benefit to adjuvant T-DM1 for those with residual disease after NST. We aimed to determine national rates of NST for patients with cT1-2 N0 M0 HER2 + BC and identify factors associated with receipt of NST vs upfront surgery with adjuvant systemic therapy (US-AST).

methodsA retrospective cohort study of women with cT1-2 N0 M0 HER2 + BC was performed using the National Cancer Database from 2016-2021. ANOVA, Kruskal-Wallis, Chi-square, Fisher's Exact tests, and a multivariable logistic regression analysis were used.

results54,449 patients met inclusion: 30,546 (56.1%) received US-AST and 19,562 (35.9%) received NST. NST utilization increased from 31.1% in 2016-17 to 43.3% in 2020-21. On regression analysis, women diagnosed in 2020-21 were more likely to receive NST (OR 1.9, 95% CI 1.8-2.0). Populations less likely to receive NST included NH-Black women (OR 0.87, 95% CI 0.8-0.95), age ≥ 70 (OR 0.7, 95% CI 0.6-0.8), increasing comorbidities (OR 0.7, 95% CI 0.5-0.9), and Medicare insurance (OR 0.8, 95% CI 0.7-0.8). Patients with cT2 disease were more likely to receive NST vs those with cT1 disease (p < 0.001).

conclusionFrom 2016-2021, national rates of NST for patients with cT1-2 N0 HER2 + BC significantly increased. Race/ethnicity and insurance type were associated with receipt of NST underscoring ongoing disparities in care. Future studies are needed to determine the impact of the disparate rates of NST utilization on oncologic outcomes, given the survival benefit with adjuvant T-DM1 in those with residual disease after NST.