The risk of blood clots in the veins of the legs or the lungs, known as venous thrombosis (VTE) is higher in cancer patients, and so is the risk of bleeding.
Whereas anticoagulant therapy lowers the risk of thrombosis recurrence, it further increases the risk of bleeding.
Previous studies suggested that the risks of dying from a thrombosis recurrence or bleeding are similar, but such findings may not apply to cancer patients.
We aimed to determine the risk of dying from a thrombosis recurrence or bleeding in patients with cancer and thrombosis.
We used administrative databases to conduct a population-based retrospective cohort study in Ontario, Canada, including patients 65 years old and older with cancer and a VTE diagnosed within 6 months of the cancer diagnosis.
We estimated the VTE recurrence and major bleeding (MB; defined as gastrointestinal or intracranial) and the 7-day mortality after VTE recurrence or MB events, as well as the ratios of the mortality for MB compared to VTE recurrence.
Between 2004 and 2014 we included 6967 VTE events (mean age 75 years, 52% male) treated primarily with low molecular weight heparin or warfarin, either alone or in combination.
At 6 months of the initial VTE there were 3% MB events and 17% VTE recurrences.
The 7-day mortality rate was 0.5% for VTE and 11% for MB with a ratio of 21.8 (95% CI 9-53).
There were no differences between anticoagulants.
This study suggests that the use of anticoagulants in patients 65 years or older with cancer-related thrombosis results in an at least 9 times higher mortality if they develop a major bleeding event, compared to a VTE recurrence.
This information should be confirmed in further studies and taken into account when designing studies and interventions in this population.