Abstract P5-12-03: Prevalence of bone loss among nonmetastatic breast cancer patients treated with aromatase inhibitors in the United States
Authors: Pirolli M , Hernandez RK , Reich A , Liede A 
Published: May 2016

Background: Adjuvant endocrine therapy compromises bone health in patients (pts) with breast cancer, leading to osteopenia, osteoporosis, and fractures (Forbes 2008). For postmenopausal women with estrogen receptor (ER) positive (+ve) breast cancer, aromatase inhibitors (AI) have emerged as the standard of care because of superior efficacy over selective ER modulators such as tamoxifen, shown in several large clinical trials. As rates of utilization and duration of AI therapy are expected to continue to increase, we report estimates of the prevalence of women with nonmetastatic breast cancer treated with AI in the United States and examine evidence of bone loss before and after AI exposure.

Methods: The Oncology Services Comprehensive Electronic Records (OSCER) database, an electronic medical record database on &gt;500,000 cancer pts from oncology practices across the US, was used to identify women with breast cancer (ICD-9 174*), ≥1 clinic visit, and confirmed AI therapy (anastrozole, letrozole, or exemestane) in 2014, excluding pts with evidence of metastases (ICD-9 196-198, stage IV, or M1 disease). OSCER is projected nationally through methods of direct estimations utilizing claims data for 1-year period prevalence. Bone loss was defined by diagnosis of osteoporosis (ICD-9 733.0), osteopenia (ICD-9 733.90), or receipt of bone therapy in 2014. Bone therapies used as proxy for bone loss were intravenous (IV) (ibandronate, zoledronic acid), or oral bisphosphonates (BPs) (risedronate, ibandronate, etidronate, alendronate), or subcutaneous anti-RANK ligand antibody (denosumab [60 mg Q6M]).

Results: It is nationally estimated that 538,630 (95% CI 519,839 - 557,422) women with nonmetastatic breast cancer were treated with an AI in 2014, representing a median of 6 prescriptions (mean 6.8). Of these, most (94%) were treated with anastrozole or letrozole, 55% were ≥65 years, and 11% took tamoxifen prior to first AI. Among women taking AI in 2014, 39% started in 2014, 24% started in 2013, and 37% have been on AI therapy since 2012 or earlier. Overall, 285,543 (53%) pts on AI therapy had evidence of bone loss, 30% of whom developed bone loss after exposure to AI therapy. Among the 338,784 women with no evidence of pre-existing bone loss, 25% (85,697) developed bone loss after initiating AI therapy (table), with 21% treated with oral and 1% IV BPs, or 9% with denosumab.

2014 prevalenceN (%)Nonmetastatic pts on AI therapy538,630At least 2 AI prescriptions in lifetime468,608 (87)Bone loss before starting AI199,846 (37)No bone loss before AI, with bone loss after AI85,697 (16)

Conclusions: This study provides current estimates of the prevalence of nonmetastatic breast cancer treated with AI in the US using real-world data, indicating that more than 535,000 women were treated with AI in 2014. Considering that 37% of pts have been on endocrine therapy since 2012 or earlier, continued use of AI will likely lead to increased pts with bone loss. These women face an increased risk of fractures, highlighting the need for intervention with antiresorptive treatments (i.e., BPs have been studied, and denosumab has a labeled indication in this setting) that may help build bone mass and counteract detrimental effects on the bone.

Citation Format: Pirolli M, Hernandez RK, Reich A, Liede A. Prevalence of bone loss among nonmetastatic breast cancer patients treated with aromatase inhibitors in the United States. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P5-12-03.