Aromatase inhibitor shows promise in reducing breast cancer recurrence

Physicians are divided on its use

New research shows that aromatase inhibitor anastrozole (Arimidex) may be more effective than tamoxifen in preventing recurrence of breast cancer.

These results from the breast cancer trial "Arimidex, Tamoxifen, Alone, or in Combination (ATAC)" were published Dec. 8 on The Lancet web site. They were also presented at the San Antonio Breast Cancer Symposium in December.

The researchers wanted to compare anastrozole to tamoxifen for five years in more than 9,000 postmenopausal women with localized breast cancer. Tamoxifen is the standard adjuvant endocrine treatment, but recurrences and side effects limit its usefulness, the researchers say. The patients were followed for a median of 68 months. The researchers found that anastrozole significantly prolonged disease-free survival and time to recurrence, and significantly reduced distant metastases and contralateral breast cancers. Fewer patients taking the anastrozole withdrew from the study compared to those taking tamoxifen. In addition, anastrozole was associated with fewer side effects; however, arthralgia and fractures increased.

The researchers conclude that the "present data suggest that it is not appropriate to wait five years to start an aromatase inhibitor." "Furthermore," they say, "the higher rates of recurrence (especially in years one to three), and the increased numbers of adverse events and treatment withdrawals associated with tamoxifen, lend support to the approach of offering the most effective and well-tolerated therapy at the earliest opportunity. Five years of anastrozole should now be considered as the preferred initial adjuvant endocrine treatment for postmenopausal women with hormone receptor-positive localized breast cancer."

Some physicians, however, think the use of anastrozole as the initial therapy may be premature. In November, a Technology Assessment Panel from the American Society of Clinical Oncology (ASCO) in Alexandria, VA, updated ASCO’s recommendations on adjuvant therapy for postmenopausal women with hormone receptor-positive breast cancer. The guidelines did not endorse the use of aromatase inhibitors as initial adjuvant therapy, and the chairman of the panel told media outlets that the new study results would not change the recommendations.

Here are the panel’s general guidelines for use of aromatase inhibitors:

  • Postmenopausal women with hormone receptor-positive breast cancer may substitute an aromatase inhibitor for tamoxifen as initial adjuvant therapy. Alternatively, women still can begin treatment with tamoxifen and plan to switch to an aromatase inhibitor after two to five years. "It not clear at this time which strategy is superior," the panel says.
  • Postmenopausal women who currently are taking tamoxifen may consider switching to an aromatase inhibitor after two to five years of tamoxifen therapy.
  • Women who switch to an aromatase inhibitor may continue this therapy for two to three more years, but no longer than five years. Women are advised that the result of treatment with an aromatase inhibitor for longer than five years has not been studied and should only be done in the context of a clinical trial.
  • There are no data to recommend taking tamoxifen after an aromatase inhibitor.

In addition, the panel says, women who develop invasive hormone receptor-positive breast cancer while taking tamoxifen for breast cancer risk reduction, and women who cannot take tamoxifen because of high risk of severe side effects, or who have tried tamoxifen and had to stop because of severe side effects, might be advised to consider using an aromatase inhibitor.