An expert panel convened at the annual meeting of the American Society of Clinical Oncology in Orlando has recommended that tamoxifen remain the standard of care for prevention of breast cancer recurrence following surgery.

They panelists also said that available data on aromatase inhibitors is insufficient to recommend their use among early stage patients outside of clinical trials.

"While recent findings on the use of aromatase inhibitors for the prevention of breast cancer recurrence are encouraging, data on long-term use of the drugs are needed before a change in the standard of care is justified," said Eric Winer, M.D., Director of the Breast Oncology Center at the Dana-Farber Cancer Institute and chair of the panel. "Patients and physicians can rest assured that tamoxifen remains the best option for use outside of clinical trials, and that it reduces the risk of recurrence and improves overall survival with manageable side effects for most women."

The panel of leading breast cancer experts was formed to conduct an assessment of available data on aromatase inhibitors, following the release of preliminary data from the ATAC (Arimidex (anastrazole), Tamoxifen Alone or in Combination) study at the San Antonio Breast Cancer Symposium at the end of 2001. The preliminary findings suggested that the aromatase inhibitor anastrazole (Arimidex) may be more effective than tamoxifen at preventing recurrence in post-menopausal early stage breast cancer patients who have undergone surgery. ASCO examined the ATAC trial, as well as the medical literature.

The ATAC study is designed to compare the benefits of anastrazole and tamoxifen over five years, and includes over 9,000 patients with early stage breast cancer who previously completed primary surgery and were candidates to receive adjuvant hormonal therapy. In a preliminary analysis conducted after a median follow-up of 33 months, 317 of the 3,125 women taking anastrazole had a relapse of their breast cancer or died, compared to 379 of the 3,116 women on tamoxifen. This represents a 17 percent reduction in the risk of disease recurrence with anastrazole treatment compared to tamoxifen. No formal analysis of the impact of anastrazole on patient survival has yet been conducted.

Although the reduction in breast cancer recurrence seen in the ATAC trial is promising, the ASCO panel determined that the lack of data on the long-term efficacy and tolerability of anastrazole makes it premature to recommend the drug for routine use. Because a five-year course of therapy is required in order for tamoxifen to provide its greatest clinical benefit, the data is not sufficiently long-term to appropriately compare the two drugs.

While incidence of serious side effects in the ATAC trial was low for both anastrazole and tamoxifen, it is possible that long-term use of anastrazole may lead to unexpected side effects. In contrast, there is extensive, long-term follow-up data on patients treated with tamoxifen and a clearer understanding of its associated risks.

The expert panel also found no evidence to suggest that women who have started a standard course of tamoxifen should consider switching to anastrazole or other aromatase inhibitors. However, for women with specific contraindications or adverse reactions to tamoxifen, the use of anastrazole may be an option. They said that healthcare providers and patients should make this decision on an individual basis, with careful consideration of all the available data.

ASCO also updated its recommendations on the use of hormonal therapies for the reduction of breast cancer risk in pre-menopausal women at elevated risk for the disease. The results of a new technological assessment support the recommendation that women age 35 and over with a five-year projected breast cancer risk of greater than 1.66 percent be considered candidates for tamoxifen.

The updated assessment, which confirms a similar ASCO recommendation from 1999, also found insufficient evidence to suggest that raloxifene be used for breast cancer risk reduction. Additionally, the assessment found no evidence to support the use of aromatase inhibitors for reduction of breast cancer risk.

SOURCE:
Annual Meeting of the American Society of Clinical Oncology, May 19, 2002, Orlando, Florida