WASHINGTON (Reuters) – Iressa, a once-promising lung cancer drug that was later shown to help only a few patients, may help some patients with breast cancer, US researchers reported last week.

Combining Iressa with the breast cancer drug Arimidex helped women survive 45 percent longer without the cancer coming back than using Arimidex alone, the researchers said.

The surprising findings are the first to show any benefit for Iressa in breast cancer, said Dr. Massimo Cristofanilli of the University of Texas M.D. Anderson Cancer Center, who led the study.

AstraZeneca Plc's Iressa, known generically as gefitinib, is in a class of drugs known as epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors.

Iressa had dramatic results in some lung cancer patients, but a 2004 study showed that it only helped about 10 percent to 15 percent of lung cancer patients.

"We initiated this study in 2003 with hopes of reducing the resistance to hormonal therapy," Cristofanilli said in a statement.

He said laboratory research had shown that women whose cancer resists the hormone-based drugs such as Arimidex and tamoxifen may have genetic mutations in the EGFR pathway.

Perhaps by attacking cancer on two fronts – through the estrogen pathway and also EGFR – it would be easier to control, Cristofanilli thought.

His team set up a study of 93 women from 30 centres across the United States and Latin America, all newly diagnosed with breast cancer that had already spread but which appeared to be the hormone-dependent type. AstraZeneca paid for the study.

The patients received either Arimidex, also sold by the Anglo-Swedish AstraZeneca and known generically as anastrozole, or Arimidex and Iressa.

The women who got both pills lived on average for 14.5 months before the tumors came back or started growing again, compared to 8.2 months in the women who took Arimidex alone.

Cristofanilli will present further details of the findings at the American Society for Clinical Oncology's annual meeting in Chicago next month.

"These findings show the possibility of adding a targeted therapy such as Iressa or others in the EGFR drug class to improve the benefit for hormonal therapy," Cristofanilli said.

Iressa was once viewed as a likely blockbuster for AstraZeneca. It is sold mainly in Asia and worldwide sales in the first quarter totalled $58 million.