New Drugs Benefit Some Breast Cancer Patients

Data from clinical trials suggest that a new class of drugs called aromatase inhibitors may be more effective then tamoxifen for treating some breast cancer patients. The data were presented at the San Antonio Breast Cancer Symposium in San Antonio (Texas, USA).

Data from a phase III study showed that compared to tamoxifen, the drug letrozole (Femara) may improve survival of postmenopausal women with locally advanced or metastatic breast cancer who are appropriate for hormone therapy. The study, involving 907 postmenopausal women, demonstrated survival rates at one and two years that gave letrozole a statistically significant survival advantage compared to tamoxifen.

The data also showed that more of the women who had begun therapy on letrozole around five years ago were still alive and free of tumor progression compared to women who were given tamoxifen. In addition, patients taking letrozole were shown to have a 78% greater chance of responding to treatment than tamoxifen patients, and the chance that their tumors would progress was 30% less. Letrozole was shown to delay progression of disease for a median of 9.4 months, compared to 6.0 months for tamoxifen.

Data from a subset of patients also showed that letrozole may be more effective than tamoxifen in treating postmenopausal women with estrogen-receptor and HER-2 positive breast cancer in the early stage of disease. Based on tissue samples from 337 such patients, tumors had a much greater response rate with letrozole (88%) than with tamoxifen (21%). Letrozole is the product of Novartis (Basel, Switzerland).

A second study presented at the symposium involved another aromatase inhibitor, anastrozole (Arimidex) and 3,125 women. The study results showed that women taking anastrozole had 17% less recurrence of cancer than women taking tamoxifen. Anastrozole is the product of AstraZeneca (London, UK).

Aromatase inhibitors block the action of the aromatase enzyme, preventing the enzyme from converting a precursor hormone, androgen, into estrogen and thereby depriving the tumor of estrogen. Because the drugs block a single pathway, there are fewer side effects. However, since the drugs affect the production of estrogen, they do not work in premenopausal women. Data also suggest that they may increase the risk of osteoporosis.
In contrast, tamoxifen blocks estrogen from docking at sites in the cancer cell called estrogen receptors, but its presence still triggers some estrogen-regulated genes to exert influence. This may blunt its effect against some breast cancers, says Novartis.



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