OBJECTIVE: Tissue inhibitor of metalloproteinases-1 (TIMP-1) has been investigated as a potential tumour marker in breast cancer. Here we investigated the correlation between TIMP-1 in tumour tissue and plasma to evaluate whether TIMP-1 in plasma is actually a surrogate marker for TIMP-1 in primary tumours. Furthermore, we assessed whether increased TIMP-1 levels in plasma could be indicative of tumour progression in patients with advanced breast cancer. METHODS: Tumour tissue and preoperatively collected plasma samples from 96 primary breast cancer patients were included together with plasma samples from 46 patients with advanced disease. TIMP-1 levels were measured by ELISA. RESULTS: TIMP-1 levels in plasma (median 81.5 ng/ml, range 41.9-174.9) and tumour tissue (median 25.4 ng/mg of total protein, range 0-110.2) from primary breast cancer patients were not correlated (r = 0.05, p = 0.6). Plasma levels of TIMP-1 in primary breast cancer patients were significantly lower than levels in patients with advanced disease (median 108.7 ng/ml, range 59.7-560.7; p < 0.0001). CONCLUSIONS: Our findings suggest that TIMP-1 release into the blood might be controlled by an active mechanism. They also point to plasma TIMP-1 as a potential marker for predicting tumour progression and for monitoring tumour burden in metastatic breast cancer patients.