Duration of neoadjuvant endocrine therapy and breast cancer outcomes.

Abstract

e12129 Background: Interest in the use of neoadjuvant endocrine therapy (NET) has increased over the past decade, and recent studies have demonstrated similar response rates compared to neoadjuvant chemotherapy. We examined the associations between duration of NET and type of surgery and change from clinical stage to pathologic stage. Methods: We used the National Cancer Data Base to identify women diagnosed with stage II-III, ER and/or PR positive breast cancer who received endocrine therapy from 2004-2014 and underwent surgery. We classified patients according to timing and duration of NET. We performed logistic regression to examine the impact of NET duration on likelihood of 1) receiving breast conserving surgery (BCS) versus mastectomy and 2) being downstaged. Downstaging was defined as pathologic stage lower than clinical stage and upstaging as pathologic stage higher than clinical stage. Results: In our sample of 159,676 patients, 6584 received NET (4.1%). NET was more frequently used in older women with multiple comorbid conditions, larger tumors, and higher nodal stage. The highest rates of NET were in academic/research or integrated network cancer programs. Of patients who underwent NET, 26.5% received it for ≤3 months, 41.0% for 3-6 months, 27.7% for 6-12 months, and 4.9% for 12-24 months. Patients who received NET for 3-6, 6-12, and 12-24 months were all significantly more likely to receive BCS versus mastectomy than patients who did not receive NET (Table). Patients who underwent NET compared to adjuvant endocrine therapy were more likely to be downstaged (Table). Conclusions: The most common duration of NET was 3-6 months, but >26% of patients received NET for less than 3 months. Longer durations of NET were strongly associated with BCS and downstaging. Further research is needed to determine the population of patients mostly likely to benefit from NET and the optimal length of treatment. [Table: see text]