Biotech giant

Genentech

(DNA)

is hoping to convince regulators that its superstar cancer drug Avastin is effective in fighting breast cancer, a disease that will kill nearly 41,000 women in the U.S. this year.

Avastin is already cleared for colorectal cancer and is often prescribed by doctors to treat other types of cancer, even those for which it hasn't been officially approved.

Now, Genentech wants to win approval for the drug, in combination with chemotherapy, as a first-option treatment for patients with locally recurring breast cancer or a case that has spread to other parts of the body.

The South San Francisco, Calif., company has submitted an application to the Food and Drug Administration covering the proposed new Avastin use and is requesting a priority review. If priority review is granted, the FDA would be expected to make a decision in six months.

Physicians are allowed to administer drugs, including Avastin, as they see fit, or "off-label," after they've been approved for a single indication.

The company's FDA submission was based on a trial involving 722 patients with previously untreated, locally recurrent or metastatic breast cancer who received either Avastin plus paclitaxel chemotherapy or chemo alone. According to the study, among participants who received Avastin, 52% fewer patients died or saw their disease get worse.

Shares of Genentech were up $1.94, or 2.5%, to $79.29 Thursday.

"In this study, Avastin, when added to paclitaxel chemotherapy, doubled the time that women with metastatic breast cancer lived without their cancer advancing, without significant added toxicities, compared to patients who received only paclitaxel," said Kathy Miller, the lead trial researcher and an associate professor of medicine at Indiana University. "This is the first time progression-free survival has been observed beyond one year in a Phase III U.S. clinical trial in patients with metastatic breast cancer."

Hal Barron, Genentech's chief medical officer, said the data support the view that "Avastin, which is designed to interfere with the blood supply to tumors, may be an important part of treating metastatic breast cancer."

Genentech has another drug, Herceptin, that it sells for a certain type of breast cancer. Used along with chemo, Herceptin is designed to treat metastatic breast cancer whose tumors have too much of a particular protein known as HER2.

After skin cancer, breast cancer is the most common cancer among women. It's also the second-leading cause of cancer death in women, after lung cancer, the American Cancer Society says.

Nearly 213,000 women in the U.S. will be diagnosed with invasive breast cancer this year. Right now, slightly more than 2 million women living in the country have been treated for breast cancer, the ACS says.