Abstract P6-13-06: Tamoxifen acceptance by DCIS patients and effect on subsequent ipsilateral and contralateral breast events

Abstract

Abstract Introduction: Existing data demonstrate that the use of endocrine therapy decreases the risk of in-breast recurrence and contralateral new primary cancers. However, the acceptance of tamoxifen is relatively low in women with DCIS, with reported acceptance rates ranging from 32% to 67%. We reported 67% tamoxifen acceptance in 2005 (Nakhlis F, JACS, p688); we now re-examine this question to assess the impact of patient and tumor characteristics, and the use of tamoxifen, on new breast events in women with DCIS undergoing breast conserving therapy (BCT) or mastectomy. Methods: We conducted a retrospective review using a prospective database; 695 patients with DCIS were identified between 1998 and 2009. Patient and tumor characteristics included age, tumor grade, tumor size, margin status, re-excision status, use of BCT, adjuvant radiation therapy (RT) and tamoxifen therapy. Women undergoing bilateral mastectomy were excluded for analysis of in-breast events. The demographic data were examined for differences in continuous variables using the Wilcoxon rank sum test, and differences in categorical variables between groups were assessed using Fisher’s exact test. Multivariate odds ratios were obtained using logistic regression. Results: The mean age of the patient population was 61.5 ± 11.4 (median and range: 61 (30-99). 44.9% of patients were over the age of 50. The median follow up time was 60 months. Among the BCT group, 58.5% of 348 women with ER+ DCIS accepted tamoxifen therapy, compared to 50.7% of 71 mastectomy patients with ER+ DCIS. 188 women (27.1%) underwent mastectomy (122 unilateral and 66 bilateral); 507 (72.9%) received BCT. Among all women with complete radiation and tamoxifen data, the number of new events was 88 (16.9%). Of these, 8 (1.5%) were in the mastectomy group, and 80 (17.9%) in the BCT group (p=0.0007). Ipsilateral events occurred in 1/99 (1%) woman undergoing mastectomy. In the BCT group complete radiation and tamoxifen data were available on 448 women, of whom 54 (12%) experienced ipsilateral events (p<0.0001). The multivariate odds ratio (OR) for ipsilateral breast events in the BCT group receiving RT+ surgery, was 0.66 (95%CI 0.25-1.71); among those receiving tamoxifen + surgery it was 0.65 (95% CI 0.20-2.1) and for the combination of RT, tamoxifen, and surgery it was 0.23 (95% CI 0.08-0.65, p=0.006). In a model that included these treatment parameters, patient age, DCIS size and grade were non-significant whereas the presence of free margins was highly significant (OR 0.27, 95%CI 0.10-0.71, p=0.008). Overall, 29% of new breast events were invasive. Contralateral events occurred in 14/467 women (3%) of BCT and mastectomy patients with hormone receptor positive DCIS, but eight of these were non-compliant. Conclusions: The use of optimal DCIS therapy (complete excision, RT, tamoxifen) decreased the odds of ipsilateral breast events by 73%, whereas RT alone or tamoxifen alone in addition to surgery were less effective. Despite relatively high acceptance of tamoxifen, lack of compliance remains an issue and will be further examined. Citation Format: Anna M Higham, Irene B Helenowski, Shruti R Zaveri, Daniel H Schneider, Nora M Hansen, Kevin P Bethke, Seema A Khan. Tamoxifen acceptance by DCIS patients and effect on subsequent ipsilateral and contralateral breast events [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P6-13-06.