Iressa Shows Promise For Treatment Of Metastatic Breast Cancer When Combined With Hormonal Therapy

These findings are surprising and represent the first positive study for Iressa in breast cancer, as well as for the entire class of drugs known as epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors, said Massimo Cristofanilli, M.D., the study's principal investigator.

Cristofanilli will present the findings at the American Society for Clinical Oncology's (ASCO) upcoming annual meeting as an oral presentation.

"We initiated this study in 2003 with hopes of reducing the resistance to hormonal therapy," said Cristofanilli. "There was a lot of preclinical work indicating that, in fact, resistance to hormonal therapy is strongly associated with an activated EGFR pathway. Also, EGFR over-expression has been associated with endocrine resistance. If there's a double blockage of the EGFR and the estrogen receptor, you may achieve better control of the disease."

The Phase II study enrolled 93 women from 30 centers across the United States and Latin America, with M. D. Anderson enrolling 20 patients. All of the women were newly diagnosed with metastatic breast cancer and were hormone receptor positive and estrogen receptor HER-2 negative. Patients were randomized to receive the aromatase inhibitor Arimidex (1 milligram) and Iressa (250 milligram) daily or Arimidex and placebo. The primary endpoint was progression-free survival.

When the study was unblinded, the researchers were surprised by the distinct findings: in the women who received Arimidex and Iressa, progression-free survival was 14.5 months, compared to 8.2 months in the women who did not receive Iressa, representing a 45 percent reduction in risk.

Additionally, of the women taking the combination, 47 percent had stable disease for more than 24 weeks and 49 percent had a clinical benefit. In contrast, 22 percent of the women had taking Arimidex alone had stable disease for more than 24 weeks and 34 percent had a clinical benefit.

Patients in the combination arm did have a higher rate of adverse events, but Cristofanilli notes that overall Iressa was very well tolerated.

"To see such a difference in such a small subset of patients was tremendously surprising," said Cristofanilli. "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, giving another option for women who are hormone receptor positive, Her-2 negative with metastatic disease."

About 60 percent of women with breast cancer are hormone receptor positive and Her-2 negative, said Cristofanilli.

Iressa, a once-daily, oral tablet, was the first in a new class of anti-cancer drugs known as epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors, to become commercially available. Iressa received FDA approval May 5, 2003 as a single agent treatment for patients whose advanced lung cancer has continued to progress despite treatment with platinum-based and docetaxel chemotherapy.

However, in 2005, after a large international study resulted in negative findings and reported numerous negative side effects, the drug's labeling was altered by the FDA. Only cancer patients who had already taken the medicine and whose physician believed it was helping them were allowed to receive the drug. No new lung cancer patients were given the drug after this time.

During this period, Iressa was being tested in clinical trials in a number of cancer types, including breast cancer. Other breast cancer trials studying Iressa, either as a single agent or when combined with chemotherapy, were mostly negative.

These negative findings impacted the accrual of the Arimidex-Iressa breast cancer study, said Cristofanilli. The study fell well short of its accrual goal of 174 women.

"Still, there's significant clinical relevance to our findings. Of course, I would advise that physicians not rush to put metastatic breast cancer patients who are hormone receptor positive and estrogen receptor negative on other drugs in this class that are readily available," said Cristofanilli. "Rather, this study should serve as a proof-of-concept. With our results, there should be a renewed interest in this class of drugs and hopefully follow-up studies in the adjuvant setting will be conducted."

The study was funded by AstraZeneca. Updated data will be presented in the oral presentation, "Breast Cancer, Metastatic."