OBJECTIVES: To describe systemic treatment of metachronous metastases and the reasons of not receiving systemic treatment in patients with breast cancer. METHODS: Patients diagnosed with breast cancer without metastasis at initial diagnosis (M0) between 2006-2008 were selected from the Eindhoven Cancer Registry. By means of active follow-up by the Cancer Registry staff until January 2012, data on development of metastatic disease, treatment, and reasons of not receiving systemic treatment were collected directly from the patient files. RESULTS: Of 1,382 patients diagnosed with M0 breast cancer, 116 (8%) developed metachronous metastases during a median follow-up of 4.4 years. Of the patients developing metachronous metastases, 86 (74%) patients received systemic treatment with a median (± SD) age of 59.7 (± 13.4) years. Of these, 46 patients (53%) received chemotherapy, 19 patients (22%) received hormonal therapy and 21 patients (24%) received a combination of chemotherapy and hormonal therapy. Median (± SD) age of the patients who did not receive systemic treatment (n=30) was 70.0 (± 15.9) years. Of the 67 patients receiving chemotherapy, 17 patients (25%) were treated with taxane containing chemotherapy as first-line treatment. Of the 30 patients without any systemic treatment, 10 patients received radiotherapy, 3 patients underwent surgery and 6 patients refrained from systemic treatment. Other reasons for not receiving systemic treatment were: extensiveness of metastases/life expectancy (n=4), death before first application of chemotherapy (n=4), high age (n=1), comorbidities (n=1) or bad experience with chemotherapy in the past (n=1). CONCLUSIONS: Of the initially M0 breast cancer patients who developed metastases during follow-up the majority received systemic treatment. A quarter of the patients did not receive systemic treatment, primarily due to other treatment policies, refraining from treatment or poor condition. This study provides more insight into the treatment of metachronous metastases in the Netherlands.