New Drug Shows Promise Against Advanced Breast Cancer

Exemestane offers superior protection compared to tamoxifen

THURSDAY, March 18, 2004 (HealthDayNews) -- The first head-to-head comparison of the drugs tamoxifen and exemestane in women with advanced breast cancer showed the latter was not only safe, it meant an average of four additional months without any progression of the disease.

Exemestane, one of a class of drugs called aromatase inhibitors, is currently approved for women whose cancer progressed while they were taking tamoxifen. Two other aromatase inhibitors are also approved in the United States -- letrozole and anastrazole.

"We're probably moving into a transition phase where we will be using these types of drugs over tamoxifen in the near future," says Dr. Jay Brooks, chief of hematology/oncology at the Ochsner Clinic Foundation in New Orleans.

This latest study comes just days after another trial showed the superiority of taking tamoxifen and exemestane sequentially for five years, as opposed to taking tamoxifen alone for the full five years.

The results of these and other trials mark a step forward in the evolution of breast cancer treatment, experts say.

"[Exemestane] will be a good choice for metastatic disease," says Dr. Robert Paridaens, lead author of the study who will present the findings March 18 at the Fourth European Breast Cancer Conference in Hamburg, Germany.

"If someone asks me is there a subgroup where it's absolutely a must to start with exemestane, I would say the high-risk patients who are estrogen-receptor-positive who already have a metastasis," he says.

For postmenopausal women with estrogen-receptor-positive breast cancer, the gold standard has been to take tamoxifen for five years after initial treatment for the tumor. Tamoxifen, which has been around for 20 years, works by interfering with the ability of estrogen to fuel tumor growth.

While many women do benefit from tamoxifen, others fail to respond and, in general, the drug seems to lose its effectiveness after about five years, experts say.

Aromatase inhibitors may be poised to take the place of tamoxifen. As their name implies, these compounds inhibit aromatase, an enzyme that helps make estrogen. Exemestane is actually slightly different from its cousins in that it has a steroidal structure.

The new study, sponsored by drug maker Pfizer, involved 382 patients from 81 medical centers in 25 countries. The women were randomly selected to receive either tamoxifen or exemestane, but the study was an "open label" one, meaning both doctors and patients knew who was taking which drug.

The researchers wanted to see if exemestane would increase progression-free survival by three months over tamoxifen. In fact, the results were slightly better than that.

Women in the exemestane group had a median progression-free survival of 10.9 months compared with 6.7 months for those in the tamoxifen group. "You gain, in the average, four months," Paridaens points out.

Exemestane also led in other categories. Among the women receiving exemestane, 7.4 percent responded completely to the treatment, versus 2.6 percent of the tamoxifen patients. Also, 36.8 percent of the exemestane participants responded partially to treatment, compared to 26.6 percent in the tamoxifen group.

Although a number of questions still need to be answered, including how long a woman should take exemestane, the drug does seem poised to take its place alongside tamoxifen, even instead of it. How quickly this happens will depend, in part, on whether insurers are willing to reimburse patients for the drug. Exemestane is more expensive than tamoxifen, experts say.

"The question of the future would be does tamoxifen have any role to play in an adjuvant setting? We don't know," Paridaens says. In any event, the spectrum of drugs for breast cancer survivors is expanding. "The number of drugs we have at our disposal is increasing. It's fantastic," he adds.

A number of other researchers also presented findings at the conference:

  • Scientists from Hong Kong have found the drug lamivudine can help prevent the reactivation of the hepatitis B virus in women undergoing chemotherapy for breast cancer. Because chemotherapy suppresses the immune system, the virus often reemerges in these women.
  • A Swedish survey found many breast cancer survivors were unsatisfied with follow-up visits, finding them too hurried, among other things. The researchers raised the possibility of training specialized nurses to oversee such visits.
  • One leading breast cancer doctor questioned the advisability of ending clinical trials early. The practice, which sometimes happens when a treatment is more successful than anticipated, means questions about long-term benefits and side effects remain unanswered.
  • Dutch researchers have concluded that, contrary to popular belief, any primary breast cancer cells can spawn secondary cancer cells which then spread throughout the body. Because the genetic profiles of the primary and secondary cells are so similar, the spreading cells are likely to respond to the same treatment as the primary tumor.

More information

The National Cancer Institute has more on aromatase inhibitors and on tamoxifen and exemestane.

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