Background: Ductal carcinoma in situ (DCIS) is a low-risk precursor lesion for which hormonal therapy (HT) has been shown in clinical trials to lower risk of subsequent (subs) breast cancer (bc) but not improve overall survival (OS). We report population-based uptake of HT and outcomes by type of local therapy. Methods: SEER-Medicare data identified women (wm) with no comorbidity, ages 66+ and diagnosed 2007-2013 with DCIS as first cancer. Wm were required to have Medicare Parts A, B & D at diagnosis. Treatments were identified with Medicare claims (2007-2014): surgery within 6 months and HT within one year of diagnosis. Outcome and survival analyses included 2007-2009 diagnoses, for adequate follow up. Subs breast events were identified: any bc and ipsilateral invasive bc (ips ibc). Local therapy included NONE, lumpectomy (BCS), BCS with radiation (w/XRT), and mastectomy (MAST). Results: 4,098 wm with DCIS were studied. 40.7% of wm received HT: 26.7% Tamoxifen, 14.0% an aromatase inhibitor. HT use varied by local therapy [BCS (32.8%), BCS w/XRT (52.0%), MAST (28.0%), NONE (19.6%), p < 0.01] but not race [white (40.4%), black (46.3%), other (38.7%), p = 0.13]. More wm ages 66-74 received HT than wm aged 75+ (45.9% v 32.7%, p < 0.01). Outcomes for the full cohort are shown (Table). For wm ages 66-74 outcomes did not differ between those having NONE v any local therapy [5yr OS (95.7% v 96.9%, p = 0.71), subs bc (0% v 4.2%, p = 0.31), subs ips ibc (0% v 1.0%, p = 0.64)]. On multivariate Cox model of wm 66-74, HT was associated with better OS (HR = 0.60, CI: 0.40-0.9992, p = 0.0497) but not marital status or age (66-69 v 70-74, HR = 1.56, p = 0.10); blacks had worse OS than whites (HR = 2.45, p = 0.01). Conclusions: In this large population-based cohort of older wm with DCIS, about half received HT. Wm who received HT had fewer subs bc and superior survival. OS for wm who elected NONE was inferior to those undergoing local therapy, though this was not significant for wm ages 66-74. These findings suggest opportunities remain to improve outcomes for wm with DCIS.

* No HT v HT