Mortality following bone metastasis and skeletal-related events among women with breast cancer: a population-based analysis of U.S. Medicare beneficiaries, 1999–2006

The aim of the study is to quantify the impact of bone metastasis and skeletal-related events (SREs) on mortality in older breast cancer patients. Using the linked Surveillance, Epidemiology and End Results-Medicare database, we identified women aged 65 years or older diagnosed with breast cancer between July 1, 1999 and December 31, 2005 and followed them to determine deaths occurring through December 31, 2006. We classified patients as having possible bone metastasis and SREs using discharge diagnoses from inpatient claims and diagnoses paired with procedure codes from outpatient claims. We used Cox regression to estimate mortality hazards ratios (HR) among women with bone metastasis with or without SRE, compared with women without bone metastasis. Among 98,260 women with breast cancer (median follow-up, 3.3 years), 7,189 (7.3%) had bone metastasis either at breast cancer diagnosis (1.5%) or during follow-up (5.8%). SREs occurred in 3,319 (46%) of women with bone metastasis. HRs for risk of death were 4.9 (95% CI 4.7–5.1) and 6.2 (95% CI 5.9–6.5), respectively, for women with bone metastasis but no SRE and for women with bone metastasis plus SRE, compared with women without bone metastasis. In analyses restricted to women with bone metastasis, the adjusted HR was 1.5 (95% CI 1.4–1.6) for women with bone metastasis plus SRE, compared with women with bone metastasis but without SRE. Having a bone metastasis, as indicated by Medicare claims, was associated strongly with mortality among women with breast cancer. This association was stronger for bone metastasis complicated by SRE than for bone metastasis without SRE.