Endocrine therapy recommendation after breast-conserving surgery for ER+ ductal carcinoma in-situ and impact on clinical outcomes.

e12619 Background: NCCN guidelines recommend consideration of 5 years of adjuvant endocrine therapy (ET) after breast conserving surgery (BCS) for ER+ DCIS to lower risk of recurrence. While rates of patient acceptance and adherence to ET are known to be low, rates of provider recommendation for ET are less understood. We aim to identify patient and tumor factors associated with provider recommendation for ET and variables associated with recurrence in patients with ER+ DCIS. Methods: Patients with ER+ DCIS treated with BCS at a single institution from 2017-2019 were included. Data was collected on clinicopathologic variables, local therapy, and recommendation and adherence to adjuvant therapy. Recommendation for ET was defined as referral to medical oncology and documented recommendation for ET. Univariate and multivariate logistic regression analyses were used to identify factors associated with recurrence. Results: Of 242 patients with DCIS,124 met inclusion criteria. Median follow up was 6.5 yrs. Most patients were non-Hispanic (79.8%), White (58.1%), and postmenopausal (70.2%) with median age of 64. Median DCIS span was 16 mm, 96.8% were unifocal, and 53.2% were intermediate grade. Most patients (70.2%) completed radiation therapy. ET was recommended to 108/124 (87.1%) patients: 46/108 (42.6%) declined, 37/108 (34.3%) took ET for 5 yrs, and 25/108 (23.1%) took ET for less than 5 yrs. Recommendation for ET was not associated with patient or tumor factors, however there was a trend toward omission of ET for current users of HRT (p = 0.09), and a trend toward ET recommendation for larger size of DCIS (p = 0.06). There were 11 (8.9%) recurrences at median 3.8 yrs, including 6 (54.5%) ipsilateral DCIS, 4 (36.4%) ipsilateral invasive carcinomas, and 1 (9.1%) contralateral invasive carcinoma. No patient experienced distant recurrence or death from breast cancer. Receipt of RT was associated with lower recurrence than no RT (3.4% vs 21.6%, p = 0.003). Use of ET for any duration was also associated with lower recurrence (0% vs 17.7%, p < 0.001). Among those who did not take ET, after adjusting for DCIS span and RT, those who declined ET were more likely to recur than those not offered ET (OR 7.94, 95% CI 1.08-176.0, p = 0.0409). Conclusions: In this series of patients with ER+ DCIS treated with BCS, providers recommended ET to a majority of patients, but uptake and adherence to ET was low with about one-third of patients completing 5 years of therapy. Any duration of ET appeared protective, and patients who declined ET were more likely to experience local recurrence than those who were not prescribed ET. While this suggests that providers seem to be safely omitting ET for some patients, future studies are needed to develop precise markers of recurrence risk that could be useful in identifying subsets of patients with ER+ DCIS who could benefit from shorter durations of ET and those who can safely omit ET altogether.