Anticoagulants and breast cancer survival, a nationwide cohort study.

Various components of the coagulation cascade have been linked to breast cancer (BrCa) progression. In vivo results suggest that anticoagulants possess anticancer properties, but there are virtually no studies in human populations. Our nationwide study explored the association between anticoagulant use and BrCa survival.All anticoagulants used from 1995-2015 in women (n=73,170) diagnosed with invasive BrCa in Finland between 1995-2013 were identified from the national prescription database; women were identified from the Finnish Cancer Registry. Cox regressions were performed to analyze BrCa survival as a function of pre- and post-diagnostic anticoagulant use; analyses were conducted for different anticoagulant subtypes and overall. Models were adjusted for age, mammography screening, tumor clinical characteristics, comorbidities, statin use, antidiabetic use, and antihypertensive use. To control for immortal time bias, post-diagnostic anticoagulant use was analyzed as a time-dependent variable.At a median of 5.8 years after BrCa diagnosis, 10,900 (15%) women had died from BrCa. In total, 25,622 (35%) women had used anticoagulants during the study period. Post-diagnostic anticoagulant use increased the risk of BrCa death (HR=1.41, 95% CI 1.33-1.49). The risk was especially high for low-molecular weight heparin, although the effect disappeared in long-term users.Anticoagulant use provides no clinical benefit for BrCa survival; however, the association between thrombosis and cancer might mask potential survival benefits.Future pharmacoepidemiological studies should adjust for anticoagulant use. Research should focus on the use of new oral anticoagulants because these are rarely studied and might be associated with improved BrCa survival.