February 20, 2007

Study Published In British Medical Journal The Lancet Shows Aromasin Improves Overall Survival In Breast Cancer Patients

Research from the Intergroup Exemestane Study (IES) published today in The Lancet shows for the first time that patients who switched to Aromasin after taking tamoxifen for two to three years were 17 percent more likely to survive and were 25 percent less likely to have their cancer recur than patients who continued to take tamoxifen for a full five years.

The U.S. lead investigator on the study is Dr. Stephen Jones, M.D., US Oncology medical director and co-chair of its breast cancer research committee. US Oncology supports one of the nation's largest cancer treatment and research networks. The US Oncology Research Network contributed nearly all of the United States participants in this trial.

Aromasin, a third-generation aromatase inhibitor, is the only anti- hormonal therapy in a single trial shown to indicate improved overall survival over tamoxifen alone. Jones and fellow researchers studied over 4,700 post- menopausal women who had been treated for early-stage breast cancer and were disease-free after two to three years of taking tamoxifen after initial treatment to prevent recurrence. Seventeen percent of hormone receptor positive patients on Aromasin had a lower risk of dying versus those who continued taking tamoxifen. Hormone receptor positive patients made up approximately 97 percent of the study population.

"Our findings in this rigorous landmark study demonstrate the improved survival associated with switching from tamoxifen to Aromasin with an excellent safety profile. This means that potentially hundreds of thousands of women are moving closer to the goal of longer survival with better quality of life," said Jones.

"Trials of this caliber conducted in the community illustrate how vital community-based oncologists are to the development of new oncology therapies," said Dr. Atul Dhir, US Oncology's President, Cancer Information & Research Group. "Our research network is pleased to have accrued the majority of patients for Dr. Jones' trial. Top cancer experts like Dr. Jones -- through their significant contributions to cancer research -- embody the US Oncology mission. They make sure all cancer patients have access to the most advanced care in the community setting and accelerate advancements in quality cancer treatment through our research network."

The study:

First mature analysis of the Intergroup Exemestane Study: a randomized trial in disease-free, post-menopausal patients with early breast cancer randomized to continue tamoxifen or switch to exemestane following an initial 2-3 years of adjuvant tamoxifen.

Researchers: R.C. Coombes, R. Paridaens, J. Jassem, C.J. Van de Velde, T. Delozier, S.E. Jones, E. Hall. L.S. Kilburn, C.F. Snowdon, J.M. Bliss, for the Intergroup Exemestane Study (IES)

Evidence of early improvements in disease-free survival (DFS) with the use of an aromatase inhibitor (AI), either instead of, or sequentially after tamoxifen have challenged five years of tamoxifen as the endocrine treatment of choice for post-menopausal women with estrogen-receptor (ER) early breast cancer. However, there is little information on the long term post-treatment effects of AIs, and whether early DFS improvements lead to real survival gains.

Four thousand seven hundred twenty-four post-menopausal patients with unilateral invasive breast cancer, disease-free on 203 years of tamoxifen, were randomly assigned to switch to exemestane (n=2352) or to continue tamoxifen (n=2372) for the remainder of a five-year endocrine treatment period. The primary endpoint was DFS. Secondary endpoints included overall survival, long-term safety and tolerability. A supplementary analysis excluded 122 patients subsequently found to have had ER negative disease and therefore ineligible.

After a median follow-up of 56 months, a total of 809 DFS events have been reported (354 exemestane, 455 tamoxifen). The unadjusted hazard ratio (HR) for DFS was 0.76 (95%CI 0.66, 0.88) p=0.0001, favoring exemestane with an absolute benefit of 3.3% (95%CI 1.6, 4.9) by the end of the treatment (i.e. 2.5 years after randomization). A reduction in risk of death was observed following a switch to exemestane (222 deaths) compared with continuation of tamoxifen (261 deaths); corresponding to a HR of 0.85 (95%CI 0.71, 1.02) p=0.08; and 0.83 (95%CI 0.69, 1.00) p=0.05 when patients with ER negative disease were excluded. Exemestane and tamoxifen were well tolerated and severe toxic effects were rare.

The conclusion shows that previously reported early DFS improvements seen following a switch to exemestane after 2-3 years of tamoxifen persist post- treatment and translate into a modest, but real, improvement in overall survival.

Additional details on the article are available upon request from US Oncology.

About the US Oncology Research Network

The US Oncology Research Network is an established community-based research operation specializing in all phases of cancer clinical trials. The research network currently has more than 536 physicians actively enrolling patients, 88 research sites, and is currently involved in 72 open research trials. The network has contributed to the development of 23 of 29 of the latest cancer-fighting drugs approved by the Food and Drug Administration for use. Since 1993, nearly 30,000 patients have participated in clinical trials managed by US Oncology network practices. For more information, visit the "Research" section under "Our Services" on the company's Web site, http://www.usoncology.com.

About US Oncology, Inc.

US Oncology, headquartered in Houston, supports one of the nation's largest cancer treatment and research networks. US Oncology provides extensive services and support to its affiliated cancer care sites nationwide to help them expand their offering of the most advanced treatments and technologies, build integrated community-based cancer care centers, improve their therapeutic drug management programs, and participate in many of the new cancer-related clinical research studies. US Oncology also provides a broad range of services to pharmaceutical manufacturers, including product distribution and informational services such as data reporting and analysis.

According to the company's last quarterly earnings report, US Oncology is affiliated with 1029 physicians operating in 411 locations, including 91 radiation oncology facilities in 35 states.

US Oncology, Inc.

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