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(AP)  Genentech Inc. began shipping its widely anticipated colon cancer-fighting drug just hours after the government approved the novel biotechnology treatment.

Avastin is designed to choke the blood supply that feeds tumors and is the first drug of its kind to be approved by the FDA. When used with chemotherapy, it has been found to extend the life of the sickest patients by an average of about five months.

Some 30 other experimental drugs based on similar technology are in various states of human testing and large drug makers such as Novartis, Bayer and Pfizer are in advanced development. Genentech also said it's experimenting with Avastin in several other forms of cancer, including kidney and lung.

The idea is that tumors must form a network of blood vessels to survive — and that shutting down that process, called angiogenesis, could fight cancer in a manner completely differently than other treatments.

That theory was pioneered by Harvard University's Dr. Judah Folkman, who made front-page news in 1998 with reports that his anti-angiogenesis drugs had cured mice of cancer. But attempt after attempt to make such drugs work in people failed.

Genentech Inc. saw its stock plummet as recently as 2002 when the drug failed to help breast cancer patients.

But in May, the South San Francisco-based company surprised Wall Street when it announced that Avastin showed promise after doctors tried it in the sickest of colon cancer patients.

Analysts expect the drug, which will cost each patient about $4,400 per month, to surpass $1 billion in sales in the next few years.

In a study of 800 people, half received intravenous Avastin in addition to routine chemotherapy. Not only was tumor growth delayed in those getting Avastin, but the Avastin patients lived about 20 months, five months longer than those getting standard treatment.

It was the first time in three decades of research that an anti-angiogenesis drug was proven to help people.

Avastin occasionally causes some serious side effects, including formation of holes in the colon that may require surgery to fix, impaired wound healing and internal bleeding, the FDA said. More common side effects are high blood pressure, fatigue, blood clots, diarrhea, appetite loss and increased risk of infection because of decreased white blood cells.