Pfizer breast cancer drug looks to be best in field

A breast cancer drug made by Pfizer Inc. increased survival rates by 63 percent compared with the standard therapy tamoxifen, researchers said on Wednesday.

The clinical trial strengthens the case for administering the newer drug, exemestane, as a first option. A study published last week showed that women recovering from breast cancer lowered their chance of developing another tumor by 32 percent if they switched to exemestane after two or three years of tamoxifen treatment.

According to the research presented this week at a breast cancer conference in Hamburg, Germany, the median survival for patients taking exemestane was 10.9 months, compared with 6.7 months for patients on tamoxifen. Pfizer provided financial support for the 382-patient study.

"These are very substantive results," said Dr. Robert Paridaens, a lead investigator in the study who began trying the drug in patients in 1989, well before it was approved. "The comparisons are significant."

Pfizer markets exemestane under the brand name Aromasin. The drug was launched in 2000 by Pharmacia, which Pfizer acquired last year, and is not one of Pfizer's top sellers.

Tamoxifen is sold under the brand name Nolvadex by AstraZeneca Plc (London:AZN.L - News) and is usually taken for five years. Sales of Nolvadex totaled $178 million in 2003, down 66 percent from 2002 as it faced cheaper generic competitors.

Tamoxifen works by blocking the hormone estrogen, which can stimulate and feed the growth of breast cancer.

By contrast, exemestane was the first approved oral therapy that binds to an enzyme known as aromatase, which normally converts the hormone androgen into estrogen in postmenopausal women.

The Pfizer drug thereby curtails the actual supply of estrogen to the cancerous tumors that are dependent on it, rather than blocking estrogen after it is already produced.

"I think that what we see here is that Aromasin, which is currently approved in women who have failed tamoxifen, also works in women who have not received tamoxifen," said Dr. Milayna Subar, medical director in Pfizer's Aromasin group.

She declined to comment on whether Pfizer would seek an additional indication for the drug as a first-line therapy.

About 44.2 percent of patients in the study had tumors that responded either partially or fully to Aromasin, compared with 29.2 percent on tamoxifen. The difference was statistically significant.

There are two other aromatase inhibitors on the market -- AstraZeneca's newer drug Arimidex and Novartis AG's (NOVN.VX) Femara -- according to Dr. Stephen Jones, who helped lead the study published in the New England Journal of Medicine last week on patients who switched to exemestane after two or three years of tamoxifen treatment.

"These (studies) are pieces of the puzzle," Jones said. "Last week and this week are two more pieces, again proving that Aromasin is a very active drug in breast cancer. The puzzle is becoming clearer now."