NEW YORK (CNN/Money) - Herceptin, Genentech's drug for fighting some late-stage breast cancer, could potentially double its sales if approved by the Food and Drug Administration to fight cancer in the early stages.

Genentech's (up $3.12 to $72.55, Research) stock rallied Tuesday on the news.

"It's a big deal for women with breast cancer," said Genentech spokeswoman Colleen Wilson. "The potential is that their cancer never comes back and spreads. It definitely has the potential to make a big impact."

Genentech said Monday that late-stage testing was completed, two years early, for use of Herceptin in causing the remission of breast cancer in its early stages. The company will submit Herceptin to the FDA within months to be approved for its new use, according to Wilson.

Test patients who used Herceptin with chemotherapy had a 52 percent better rate of remission than patients who used chemotherapy without the drug, the company said.

"We could see Herceptin at a billion dollars [in annual sales] in the next three or four years," said Sena Lund, analyst for Cathay Financial. "This opens up an entirely different market."

Sales for Herceptin, a drug used to prolong survival for women with metastasized breast cancer, totaled $483.2 million in 2004, a 14 percent jump from $424.8 million in 2003, according to Genentech. The company's totaled $3.7 billion in 2004 sales.

Herceptin is a personalized medicine used by patients with a specific genetic makeup, called Her2, that makes them eligible for treatment. The company said about 25 percent of women with metastasized breast cancer can use the drug.

Herceptin can be used to treat the 32,000 Her2-positive women diagnosed with metastatic breast cancer every year, the company said. This patient base would more than double if Herceptin is approved by the FDA to treat early-stage breast cancer in conjunction with chemotherapy.

"Longer term, you may see less women who are treated in the metastatic setting," said Wilson. "The potential is that their cancer never comes back and spreads."

She would not speculate as to when the drug might be available for its expanded use, but Sund said the drug could be approved by mid-2006.

Matthew Geller, an analyst for CIBC World Markets, spoke favorably of the stock -- but he considers it expensive.

"We think it's a great stock," said Geller. "But we can't say that the stock is cheap, trading at over 80 times earnings. We get a little bit of acrophobia."

Despite the positive news surrounding Herceptin, Geller said Avastin remains the most promising product for Genentech because it treats a more general population of patients diagnosed with colorectal cancer, rather than a gene-specific minority.

Genentech announced April 14 that Avastin passed last-stage testing in treating metastatic breast cancer in conjunction with chemotherapy.

Avastin was approved by the FDA on Feb. 26, 2004 and totaled $554.5 million in sales last year.

About 211,000 women are expected to be diagnosed with breast cancer in 2005, according to the American Cancer Society. Approximately 40,000 are expected to die of the disease.