Genentech Inc. said on Monday its breast cancer drug Herceptin improved survival in certain women with early-stage cancer who underwent surgery.

The National Cancer Institute said the promising results led it to call an early halt to two trials comparing Herceptin plus chemotherapy to chemotherapy alone in women who had surgery for breast cancer that had not spread.

Patients who received Herceptin and chemotherapy had a 52 percent decrease in disease recurrence compared to those treated with chemotherapy alone, according to the institute.

“This is a major advance for many thousands of women with breast cancer,” NCI Director Dr. Andrew von Eschenbach, said in a statement. “These results are one more example that we are at a major turning point in the use of targeted therapies to eliminate suffering and death from cancer.”

Interim analysis of the two trials also found an improvement in overall survival, according to Genentech, the world’s second-largest biotechnology company.

Herceptin is an antibody-based drug, which has been on the market since 1998 as a treatment for the 25 percent to 30 percent of breast cancer patients who have tumors that generate a protein called HER-2 and whose cancer has spread beyond the breast.

These tumors tend to grow faster and are generally more likely to recur than tumors that do not carry the protein.

Herceptin had sales of $483 million last year.

The results “confirm how important it is for targeted therapy to be used as early as possible,” said Susan Desmond-Hellmann, Genentech’s president of product development.

Hellmann said further follow-up was necessary. But based on the strength of the results, Genentech will enter discussions with U.S. regulators about an additional approval for Herceptin.

Some 34,000 patients will be eligible for Herceptin therapy in the adjuvant breast cancer setting, Mark Schoenebaum, an analyst at Bear Stearns, said in a report on Monday. He said that equates to a market of $800 million, although there are still key unknowns - such of the duration of therapy.

Hellmann noted that Herceptin raises the risk of serious cardiac events, including heart failure, by 3 percent to 4 percent.

Genentech’s shares have risen 58 percent over the last six weeks, driven largely by positive trial results for Avastin, another of its cancer drugs, in both lung cancer and breast cancer.