Utilization, duration, and outcomes of neoadjuvant endocrine therapy in the United States.

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To evaluate if real-world utilization of neoadjuvant endocrine therapy (NET) is associated with similar rates of response and breast conservation surgery (BCS) compared to neoadjuvant chemotherapy (NAC). Our population-based assessment used the National Cancer Data Base to identify women diagnosed with stage II-III, hormone receptor (HR)-positive BC who underwent surgery and received endocrine therapy from 2004 to 2014. Women were categorized by receipt of NET, NAC or no neoadjuvant therapy. We used logistic regression to assess differences in outcomes between therapies using inverse propensity score weighting to adjust for potential selection bias. In our sample of 211,986 women, 6584 received NET, 52,310 received NAC, and 153,092 did not receive any neoadjuvant therapy. After adjusting for multiple relevant covariates and cofounders, there was no significant difference between NET and NAC with regard to BCS [odds ratio (OR) 0.91; 95% confidence interval (CI) (0.82-1.01)]; however, women who received NET were significantly less likely to achieve pCR [OR 0.34; 95% CI (0.23-0.51)] or a decrease in T stage [OR 0.39; CI (0.34-0.44)] compared to women treated with NAC. Patients who received NET for ≥ 3months had higher odds of BCS (OR 1.59; 95% CI 1.46-1.73) and downstaging (OR 1.79; 95% CI 1.63-1.97) compared to patients who did not receive neoadjuvant therapy. Women who received NET had similar rates of BCS compared to women who received NAC. Those who received NET for longer treatment durations had increased odds of BCS and downstaging compared to women who did not receive neoadjuvant therapy.