Multivariate Cox regression model for possible factors influencing TTP of patients with metastatic breast cancer. Age was included as a continuous variable. ER/PR status was considered positive if either of the receptors was positive and negative if both were negative. Line of treatment variable compares patients who receive vinorelbine containing treatment as first line metastatic therapy and those receiving it as second or later line. Sites of metastases variable compare patients with bone metastases only and those with other sites also present.