Acquired resistance to activated protein C in breast cancer patients.

In 56 women with a lymph-node-positive breast carcinoma and 28 matched healthy control subjects, the sensitivity to activated protein C (APC-sr) was determined with an APC resistance test that quantifies the effect of APC on thrombin generation initiated via the extrinsic coagulation pathway. Carriers of the Factor V Leiden mutation were excluded from the study. Significant resistance to APC was found in the breast cancer patients: median APC-sr 2.02 vs 1.03 in the healthy control subjects (P < 0.001). No difference in APC-sr was found between patients with metastases and without metastases. In patients with metastases, protein S levels were significantly elevated compared with patients without metastases and healthy control subjects: 108.0%vs 96.0% and 94.5% (P = 0.008 and P = 0.007). The APC-sr correlated with protein S in the control subjects and in patients without metastases but not in patients with metastases. The disturbance of the haemostatic balance probed by the tissue-factor-based APC resistance test might contribute to the cancer-related hypercoagulability.