Primary and secondary distant metastatic breast cancer: two sides of the same coin

This study evaluated the differences between breast cancer (BC) patients who present with primary distant metastatic disease (PMD) and those who develop distant metastases during the course of their illness (secondary metastatic disease [SMD]) with regard to clinicopathological characteristics, patterns of metastatic sites, palliative therapy and survival.

Based on a cohort of patients with newly diagnosed BC (n = 1459), we analyzed all patients who had PMD (n = 92, 6.3%) and those who developed SMD (n = 277, 20.3%).

There were no significant differences with regard to the patient's age in which metastatic disease had been diagnosed (PMD/SMD: 64 years/66 years, p = 0.19). The SMD group had more often triple-negative carcinomas (25.5%/7.3%, p = 0.019); there were no significant differences with regard to grading (p = 0.61), HER2 status (p = 0.67) and hormonal receptor status (p = 1.00). The mean number of metastatic locations was similar (2.3/2.3, p = 0.91). While patients with PMD usually initiated systemic therapy, patients with SMD received systemic therapy after diagnosis of metastatic disease less often (16.4%/2.6%, p < 0.001). Both groups received palliative chemotherapy similarly often (PMD/SMD: 62.8%/63.3%, p = 1.00). The mean number of palliative therapy lines was similar (PMD/SMD: 2.8/3.2, p = 0.39). Compared to patients with SMD, patients who had PMD had a significantly improved metastatic disease survival (p < 0.001). The one-year, two-year and five-year survival rates were as follows: 76.9%/60.3%, 58.2%/43.0%, 23.1%/10.6%. The median survival times were 18.5 months and 32 months.

The poorer prognosis of patients with SMD may be explained by differences in clinicopathological features of the tumor, metastatic patterns, the use palliative therapy and drug resistance of the tumor cells which occurs in therapy-naïve PMD patients at a later phase of the disease course.