Herceptin, a breast cancer drug developed by Roche and its U.S. biotechnology arm Genentech Inc., helps women fight an aggressive form of early-stage breast cancer after surgery, a study showed.

The study was the third set of positive data released this week on the drug.

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

In a late-stage study involving women in 39 countries, Herceptin was shown to improve disease-free survival in patients with HER-2-positive early-stage breast cancer - or cancer which has not spread around the body - when used with chemotherapy.

The results were taken from the interim or mid-stage analysis of a Phase III trial, Roche said in a statement.

Earlier this week, Roche and Genentech said an interim analysis of two large trials in the U.S. in patients with early-stage breast cancer - this time with specific forms of chemotherapy - showed similar positive results.

These two trials, in women who had surgery for their cancers, were stopped early after the drug plus chemotherapy was shown to reduce disease recurrence compared with those treated with chemotherapy alone.

“The combined data from over 8,000 patients analyzed so far make a compelling case for Herceptin as an optimal treatment in HER2-positive early breast cancer and has the potential to change the way breast cancer is managed,” Roche Pharma Chief Executive William Burns said in a statement.

Analysts upgraded their peak sales estimates for Heceptin in the wake of the U.S. study data, which showed that the drug, when used with chemotherapy, cut the rate of disease recurrence by 52 percent. Overall survival was also improved.

HER-2 positive early-stage breast cancer affects around 20 or 30 percent of women with breast cancer.