Background: Bone is a common site of metastatic involvement in patients (pts) with BC. Bony metastases (mets) are often associated with SREs (spinal cord compression [SCC], pathologic fracture [PF], surgery to bone [SB], radiotherapy to bone [RT]). Skeletal complications cause significant morbidity and mortality. Current estimates of SRE risk come principally from randomized clinical trials. Information from routine clinical practice is limited. Methods: Using the tumor registry and electronic data stores at a large U.S. Midwest healthcare system that serves approximately 800,000 persons, we retrospectively identified all pts aged ≥18 yrs with primary BC and newly diagnosed bone mets between 1/1/95 and 12/31/09. Electronic medical records were reviewed by trained abstractors for evidence of SREs between date of bone mets diagnosis and death, loss to follow-up, or end of study. Cumulative incidence of SREs was estimated in the presence of competing risk of death. Results: We identified a total of 378 pts with primary BC and newly diagnosed bone mets; 87 pts had evidence of SREs at initial diagnosis of bone mets and were excluded from the analyses. Among the remaining 291 pts, mean (SD) age was 58.2 yrs (14.3 yrs), and 99% were women; 48% were African-American and 46% were Caucasian. Median duration of follow-up after diagnosis of bone mets was 16.1 months (mos). At 12 mos, cumulative incidence of SREs was 44.5% (SCC, 5.2%; PF, 21.0%; SCC and/or PF, 23.3%; SB, 7.6%; RT, 34.3%) (Table). Corresponding figures at 24 mos were 53.8% (SCC, 7.5%; PF, 29.3%; SCC and/or PF, 32.5%; SB, 9.4%; RT, 41.7%). Approximately one-half (45.0%) of study subjects received intravenous bisphosphonates prior to SRE. Conclusions: Pts with BC in routine clinical practice are at high risk of SREs following initial diagnosis of bone mets.

Cumulative incidence of SREs in pts with BC and bone mets (1995-2009), by type of SRE.

Time since Dx of bone mets (mos)	No. alive*	SCC	PF	SCC and/or PF	SB	RT	Any SRE
6	239	2.8%	16.4%	17.4%	6.1%	28.5%	37.1%
12	210	5.2%	21.0%	23.3%	7.6%	34.3%	44.5%
18	179	5.2%	25.3%	27.1%	9.4%	38.5%	49.2%
24	151	7.5%	29.3%	32.5%	9.4%	41.7%	53.8%

*At beginning of interval.