Prognostic Factors in Patients with Metastatic Breast Cancer with Bone‐Only Metastases

BACKGROUND. Patients with metastatic breast cancer with bone‐only metastases (BOM) are a unique patient population without consensus regarding high‐risk characteristics, which we sought to establish. METHODS. We identified 1,445 patients with BOM followed for at least 6 months at MD Anderson Cancer Center from January 1, 1997, to December 31, 2015. RESULTS. Seventy‐one percent (n = 936) of the 1,325 patients with BOM with available pain characterization were symptomatic at time of BOM diagnosis. Pain was more common in patients with lytic compared with blastic or sclerotic metastases (odds ratio [OR], 1.79; 95% confidence interval [CI,] 1.26–2.53) and multiple versus single bone metastases (OR, 1.37; 95% CI, 1.03–1.83). Poorer overall survival (OS) was also noted in patients with multiple bone metastases (median OS, 4.80 years; 95% CI, 4.49–5.07) compared with single bone metastasis (median OS, 7.54 years; 95% CI, 6.28–10.10) and in patients with metastases in both the axial and appendicular skeleton (median OS, 4.58 years; 95% CI, 4.23–4.96) compared with appendicular‐only (median OS, 6.78 years; 95% CI, 5.26–7.96) or axial‐only metastases (median OS, 5.62 years; 95% CI, 4.81–6.69). Black/non‐Hispanic patients had poorer outcomes, and patients aged 40–49 years at time of breast cancer diagnosis had significantly better OS compared with both younger and older patient groups. CONCLUSION. Overall, several risk features for decreased OS were identified, including multiple bone metastases and both axial and appendicular skeleton involvement. Multiple bone metastases and lytic bone metastases were associated with increased pain. IMPLICATIONS FOR PRACTICE. Patients with metastatic breast cancer and bone‐only metastases (BOM) represent a poorly characterized patient subset. The ability to identify unique patient characteristics at time of BOM diagnosis associated with increased morbidity or mortality would allow for recognition of patients who would benefit from more aggressive therapy. In this study, the largest sample of patients with BOM thus far reported is characterized, highlighting several higher‐risk BOM groups, including those with multiple bone metastases and bone metastases in both the axial and appendicular skeleton at time of BOM diagnosis. In addition to tailoring current practices for these high‐risk patients, ongoing studies of these patients are indicated.