Adherence to extended adjuvant endocrine therapy following Breast Cancer Index (BCI) testing in women with early-stage hormone receptor (HR)-positive breast cancers.

Abstract

527 Background: Evidence suggests continuing endocrine therapy (ET) beyond 5 years (yr) may reduce breast cancer recurrence in early stage HR+ breast cancers. Given the modest benefit and potentially serious adverse effects of extended ET (EET), improved approaches to identify patients who are at increased risk of late distant recurrence and who derive benefit from EET are critical. Guidelines recommend shared decision-making between oncologists and patients. The adherence rate to EET by 5 yr is only 50-60%. BCI is a gene-expression assay used to predict late distant recurrence and is predictive of benefit from EET. We assessed adherence to EET in women who had BCI testing. Methods: Women with stage I-III HR+ breast cancer s/p 3.5 yr of adjuvant ET and had BCI testing at our institution (8/2013-7/2015) were included. Pts who had < 4 yr of follow-up since BCI testing were excluded. Information including demographics, tumor characteristics, treatment history, number DXA scans, history of osteopenia/osteoporosis were collected. Data on medication adherence was based on prescriptions in the electronic health record. Results: 102 pts were included in our analysis. The median age was 61yr (46-89 yr). The majority of pts had stage I (63%), N0 (77%) and HER2- (90%) disease. 50 pts (46%) received chemotherapy. 44 (43%) received tamoxifen and 79 (77%) had an aromatase inhibitor. BCI categorized 61 (60%) pts as low risk, 26 (25%) as intermediate, and 15 (15%) as high risk for late distant recurrence. 61 (60%) and 41 (40%) pts were predicted to have low and high likelihood of benefit from EET, respectively. All 15 (100%) pts categorized as high risk for late recurrence were predicted to have a high likelihood to benefit from EET; all were recommended to continue EET by their oncologist and all 15 elected EET. 11 (73%) completed 10 yr or were on EET at last follow-up. Of the 4 (27%) pts who stopped before 10 yr, 1 pt had metastatic recurrence and 3 had intolerable side effects. Pts on EET underwent an avg of 1.91 DXA scans, compared with 1.23 for those who stopped ET at 5 yr (p = 0.003). At a median follow-up of 10 yr from diagnosis, there were 2 metastatic (1/15 in the high risk and 1/26 in the intermediate risk group) and 1 local recurrence (1/61 in the low risk group). Conclusions: In pts who continued ET beyond 5 years based on BCI testing and discussion with their oncologist, the rates of adherence and persistence to EET were higher than those previously published. EET may increase the number of DXA scans performed.