Iressa Shows Promise in Breast Cancer

CancerWise - July 2008

Iressa® (gefitinib), a drug formerly approved as a second-line treatment for lung cancer, enhanced the effectiveness of hormonal therapy for the treatment of specific types of metastatic breast cancer, according to a study presented June 1 at the American Society for Clinical Oncology’s annual meeting.

Significance of results

The findings of the Phase II clinical trial, led by M. D. Anderson researchers, are surprising and represent the first positive study for Iressa in breast cancer, says Massimo Cristofanilli, M.D., the study’s principal investigator and assistant professor in the Department of Breast Medical Oncology.

Research methods

The randomized 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, with tumors that were hormone receptor positive and HER2-negative.

In the general population of women with breast cancer about 60% are hormone receptor positive and HER2-negative, Cristofanilli says.

Patients in the study received daily doses of either:

• Arimidex® (anastrozole) and Iressa
• Arimidex and a placebo

Arimidex is an aromatase inhibitor, a class of drugs that binds to and inhibits aromatase, the protein that helps produce estrogen. Estrogen is known for fueling the growth of cancer cells.

Primary results

Women who received Arimidex and Iressa experienced progression-free survival of 14.5 months, compared to 8.2 months in the women who received Arimidex without Iressa.

Of the women taking the combination:

• 47% had stable disease for more than 24 weeks
• 49% showed a clinical benefit

Of the women taking Arimidex alone:

• 22% had stable disease for more than 24 weeks
• 34% showed a clinical benefit

“To see such a difference in such a small subset of patients was tremendously surprising,” Cristofanilli says. “These findings could potentially give another treatment option to women with metastatic disease who are hormone receptor positive and HER2-negative.”

Patients in the Arimidex and Iressa arm did have a higher rate of side effects, but Cristofanilli notes that overall, Iressa was very well tolerated.

Background

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 approval May 5, 2003, from the U.S. Food and Drug Administration (FDA) as a single-agent treatment for patients whose advanced lung cancer has continued to progress despite treatment with chemotherapy.

However, in 2005, after a large international study resulted in negative findings and 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, Cristofanilli says. The study fell well short of its accrual goal of 174 women. “Still, there’s significant clinical relevance to our findings.”

What’s next?

“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,” Cristofanilli says. “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.”

— Adapted by Darcy De Leon from an M. D. Anderson news release

M. D. Anderson resources:

• Nellie B. Connally Breast Center

Other resources:

• Aromatase Inhibitors Come of Age (National Cancer Institute)