Canadians with a certain form of breast cancer may be prescribed an expensive cancer drug in combination with chemotherapy.

Avastin (bevacizumab) works by restricting the growth of blood vessels that supply tumours with nutrients and oxygen.

Health Canada has approved the use of Avastin for patients with a type of metastatic breast cancer, the drug's manufacturer, Hoffmann-La Roche Canada, said Wednesday.

"In the study, patients on the Avastin-paclitaxel combination therapy experienced a doubling of their time living without the disease advancing," said Dr. Karen Gelmon, a medical oncologist at the BC Cancer Agency and a professor of medicine at the University of British Columbia.

Health Canada previously approved the use of Avastin in people with colorectal cancer that has spread to other sites. Regulators in the U.S. and Europe approved it for treatment of metastatic breast cancer in 2008 and 2007.

In Canada, the drug is approved for HER2-negative breast cancers.

HER2 is a protein that is over-expressed by certain tumours, and can speed up the formation and growth of tumours.

The company said it is continuing to study Avastin in early-stage breast cancer, and for other types of tumours, such as prostate, kidney, pancreatic and ovarian cancer.

As a colorectal cancer treatment, Avastin costs thousands of dollars a month, and not all provinces pay for it.

In 2008, an estimated 22,400 Canadian women were diagnosed with breast cancer and approximately 5,300 died from the disease.