Characterization of bone only metastasis (BOM) patients (pts) with respect to tumor subtypes (TS).

Abstract

1072 Background: Metastatic breast cancer (MBC) pts with BOM are a unique population with limited characterization. Our goal was to characterize the TS of BOM pts, evaluating differences in sites and types of bone metastases (BM), treatment, and survival. Methods: We identified pts followed at MD Anderson Cancer Center from 01/01/1997 to 12/31/2015 for at least 6 months with a BOM diagnosis as first site of metastasis (met). TS was assessed by initial biopsy immunohistochemistry (IHC) (Table 1) with hormone receptor (HR) + defined as ER or PR >10%. Results: We identified 1445 pts with BOM, 1049 with initial biopsy IHC available to group into TS (Table 1). Among BOM pts, the majority had multiple BM at diagnosis (1141/79%), most in both the axial (Ax) and appendicular (App) skeleton (53%). Of the 808 pts with BM categorized on imaging at diagnosis, the majority were lytic (389/48%), with 21% sclerotic, 18% mixed, and 12% blastic. Time from breast cancer diagnosis to first met differed significantly by TS, χ2(3) = 94.33, P< .0001, with median time to met longer for pts with blastic (3.08 years; 95% CI 2.03, 4.24) versus lytic lesions (1.75 years; 95% CI 1.27, 2.17). Conclusions: BOM patients are a unique MBC subpopulation, more commonly found in luminal TS patients. Our study demonstrates prognostic differences in BOM pts specific to TS and emphasizes the need for further study of BOM patients. [Table: see text]