Genentech says that the US Food and Drug Administration has approved an update to the product label for its highly-touted colorectal cancer agent, Avastin (bevacizumab), which will now include a warning about an increased risk of serious and potentially fatal blood clots in patients taking the drug.

Genentech sent a letter to doctors back in August last year, warning them of an increased risk of serious arterial thromboembolic events – including stroke, transient ischemic attacks, heart attack, angina [[16/08/04a]]. It notes that an analysis of 1,745 patients treated in Avastin clinical trials showed that ATEs occurred in 4.4% of those treated with Avastin, compared with 1.9% of patients who received chemotherapy alone – some of these events were fatal. Patients over the age of 65 face the highest risk.

Avastin, which was approved by the FDA last February [[27/02/04a]], has been touted as a potential $2 billion dollar earner [[02/03/04c]]. In trials, Avastin-treated patients lived on average 30% longer than those given chemotherapy alone (20.3 months versus 15.6 months) [[03/06/03a]], and the product has already become Genentech’s second biggest selling product, behind the non-Hodgkin’s lymphoma therapy, Rituxan (rituximab), bringing in $183 million during the quarter [[07/10/04b]]. European approval is expected to follow early this year after the product won the backing of the continent’s advisory panel back in October [[22/10/04e]].