The effects of an aggressive breast tumor on thrombosis after antithrombin downregulation in a hypercoagulable mouse model

BACKGROUND: Despite improvements in therapy, breast cancer still contributes to high mortality rates. Survival of these patients becomes progressively worse upon diagnosis with cancer-associated thrombosis (CAT). Unfortunately, the mechanism causing CAT has remained unclear. OBJECTIVE: Set up an acute and non-invasive hypercoagulable mouse model with an aggressive breast cancer and study the mechanism of cancer-associated thrombosis. METHODS: Mice were grafted with the aggressive breast cancer cell line MDA-MB-231 or sham-treated. Subsequently, an acute imbalance in coagulation was introduced by injecting a synthetic small interfering (si) RNA targeting hepatic Serpinc1 to knockdown antithrombin - a condition known to predispose to cause a hypercoagulant state in vivo. RESULTS: Silencing Serpinc1 with siRNA decreased plasma antithrombin levels. siRNA treatment had no short-term effects on tumor characteristics, but increased distant metastasis within the timeframe of this study. The systemic pro-inflammatory status, with elevated platelet counts and fibrinogen levels in tumor-bearing mice, was also not affected by antithrombin silencing. While elevated fibrin deposition in the liver upon Serpinc1 targeting was not significantly affected by the presence of breast cancer, knockdown of antithrombin did significantly increase intratumoral fibrin deposition and inflammation. Surprisingly, in the presence of an aggressive tumor, a protective outcome with less clinical features coinciding with venous thrombosis were observed in mice with antithrombin knockdown. CONCLUSION: We conclude that the presence of a breast tumor protects hypercoagulant mice from severe consumption of coagulation factors after lowering hepatic antithrombin levels, possibly due to elevated platelet counts. However, the consequences on cancer-associated thrombosis remained inconclusive.