Analysis of clinicopathological factors associated with bone metastasis in breast cancer

Breast cancer is the second leading cause of cancer death in women today. Once breast cancer metastasizes to bone, mortality increases. Thus, there is an urgent need to identify patients with high risk of bone metastasis, and to find predictive factors for the occurrence of bone metastasis at an earlier stage of breast cancer. Three hundred and sixty patients with pathologically proved breast cancer visiting the Department of Nuclear Medicine for whole body bone scan from January 2006 and January 2009 were investigated in this study. Clinicopathological information was obtained, which consisted of age, menopausal status, clinical staging, lymph node stage, histological grade, the expression of estrogen receptor (ER), progesterone receptor (PR) and epidermal growth factor receptor 2 (HER2). Correlation between bone metastasis and the associated factors was tested by using the Chi-square test. A Cox multivariate analysis was used to assess the factors which independently contributed to survival after bone metastasis in breast cancer patients. Survival curves were drawn for metastasis-free interval and the independent factors which contributed to survival, using the Kaplan-Meier method. Twenty-four patients were excluded from subsequent analysis. Three hundred and thirty-six enrolled patients ranged in age from 22 to 77 years (mean, 47.8 years). ER/PR status [ER(+) vs. ER(-), χ (2)=4.328, P=0.037; ER(+)PR(+) vs. ER(+)PR(-), χ (2)=4.425, P=0.035] and histological grade (χ (2)=7.131, P=0.028) were significantly associated with bone metastasis. ER status (x (2)=8.315, P=0.004) and metastasis-free interval (χ (2)=6.863, P=0.009) were independent prognostic factors for survival in breast cancer patients with bone metastasis. Our study suggested that ER/PR status and histological grade are risk factors for the development of bone metastasis in breast cancer patients. However, ER status and metastasis-free interval are independent prognostic factors for survival in breast cancer patients with bone metastasis. Breast cancer bone metastasis has its unique characteristics, which is helpful to choose the appropriate treatment for breast cancer patients with bone metastasis.