Exemestane to Prevent Breast Cancer Recurrence Similar to Anastrozole

Zosia Chustecka

December 09, 2010

December 9, 2010 (San Antonio, Texas) — Final results from a huge study comparing 2 aromatase inhibitors head to head as adjuvant therapy in postmenopausal women with hormone-receptor-positive breast cancer found no difference between the 2.

This was the first definitive trial to compare a nonsteroidal irreversible aromatase inhibitor, exemestane (Aromasin, Pfizer) with the steroidal reversible aromatase inhibitor anastrozole (Arimidex, AstraZeneca). The final results, reported here today at the 33rd Annual San Antonio Breast Cancer Symposium (SABCS), show no difference between the 2 in their ability to reduce the risk for breast cancer recurrence and death from breast cancer.

Dr. Paul Goss

"The survival curves were superimposable," principle investigator Paul Goss, MD, from the Massachusetts General Hospital Cancer Center in Boston, told the meeting.

Exemestane is not approved for up-front 5-year adjuvant therapy, whereas anastrozole is. These latest results, from the final analysis of the MA27 study, show that "exemestane is comparable to anastrozole and provides a new option for 5-year adjuvant up-front therapy," Dr. Goss said.

The hypothesis at the start of the trial was that exemestane, because it is irreversible and more potent, would show a survival advantage over anastrozole.

The MA27 trial involved 7576 postmenopausal women (median age, 61 years) with hormone-receptor-positive breast cancer randomized to receive anastrozole (1 mg/day) or exemestane (25 mg/day). Another part of the trial randomized these women to celecoxib or placebo, but that part of the trial was stopped in 2004 when concerns about the cardiovascular toxicity of the coxibs reached their peak after the withdrawal of rofecoxib (Vioxx).

The final results presented here show no significant difference in survival between the 2 groups. Both groups showed a 91% overall survival rate after more than 4 years of follow-up, he said.

The 2 drugs have different adverse-effect profiles. Exemestane was associated with less vaginal bleeding than anastrozole, a rare but significant adverse event, Dr. Goss noted, as well as less hypertriglyceridemia, hypercholesterolemia, and self-reported osteoporosis, although the data on fractures were similar for both drugs.

However, exemestane was associated with more cases of acne and masculinization than anastrozole, which again are rare but significant adverse events, and with more cases of elevated levels of liver enzymes and bilirubin.

The 2 drugs also differ in cost, "which is the elephant in the room," said Steven Vogl, MD, a clinician from the Bronx,New York, during the question and answer session. He said that in New York, anastrozole is now available generically for around $16, whereas exemestane is not off patent yet and costs around $400. "It's a no-brainer," he said.

After the presentation, Dr. Vogl received a small award from the SABCS committee for his contribution to the discussions over the years. Dr. Vogl has been attending this meeting for years, and always makes a useful contribution to the discussion with the "insightful questions" he asks, said C. Kent Osborne, MD, from Baylor College of Medicine in Houston, Texas, who was program chair for the meeting.

Dr. Goss pointed out that the different aromatase inhibitors are coming off patent at various times in various countries around the world, and so prices likely differ from region to region.

Dr. Goss reports receiving funding from Pfizer. Dr. Osborne has disclosed no relevant financial relationships.

33rd Annual San Antonio Breast Cancer Symposium (SABCS): Abstract S1-1. Presented December 9, 2010.

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