The anti-cancer drug Avastin increases the risk of blood clots in the legs and lungs by 33 percent, according to an analysis published by US researchers Wednesday.
The study examined results of 15 clinical trials with Avastin, made by the Swiss firm Roche, involving 7,956 patients with advanced solid tumors.
The risk of developing venous thromboembolism was 33 percent greater in patients treated with the drug, bevacizumab, than in those who were not, according to Shobha Rani Nalluri, a doctor at Stony Brook University in New York state who led the study.
The appearance of blood clots varied among patients with different types of cancer.
The incidence was highest among patients with colorectal cancer, at 19.1 percent, and lowest for patients with renal cancer, at three percent. For breast cancer cases, it was 7.3 percent.
The growth of new blood vessels helps spread cancer and Avastin is designed to fight the disease by inhibiting the proliferation of new blood vessels.
But the results of the study showed the need for doctors and patients to understand the risks associated with the drug, the authors wrote.
"Our meta-analysis of 15 RCTs (randomized control trials) has ... demonstrated that bevacizumab may be associated with a significantly increased risk of venous thromboembolism in patients with a variety of metastatic solid tumors," the researchers wrote.
"This finding will help physicians and patients to recognize the risk of venous thromboembolism with the administration of bevacizumab," as the problem was more difficult to detect in previous individual trials, it said.