For patients with a common type of breast cancer known as ductal carcinoma in situ (DCIS), the drug Arimidex® (anastrozole) may provide better protection against recurrence than tamoxifen. These findings were presented at 2015 Annual Meeting of the American Society of Clinical Oncology (May 29–June 2, Chicago, Illinois) and published in the Journal of Clinical Oncology.

Ductal carcinoma in situ is an early stage of breast cancer in which abnormal cells are found within a breast duct but have not spread outside of the duct to other tissues in the breast. It is most commonly detected by screening mammography. If not treated, some cases of DCIS may progress to invasive breast cancer.

For more than a decade, tamoxifen has been the medication most used to prevent recurrence among postmenopausal women with estrogen-positive DCIS. Arimidex, however, has emerged as a potentially more effective alternative to tamoxifen. Both medications work to stop estrogen from stimulating cancer to come back, but function in different ways: tamoxifen blocks estrogen from attaching to cancer cells, while Arimidex suppresses the body’s production of estrogen.

Researchers from several U.S. institutions recently compared Arimidex with tamoxifen as prevention against recurrence in postmenopausal women with estrogen-positive DCIS. Their study included 3,104 patients who had undergone treatment for DCIS with lumpectomy and radiation and had no evidence of cancer remaining. Over the course of five years, patients received either 1 mg per day of Arimidex or 20 mg per day of tamoxifen.

After 10 years, both drugs appeared to help reduce breast cancer recurrence. The patients who took Arimidex, however, had a lower incidence of recurrence compared with those who took tamoxifen. Specifically, 93.5% of patients in the Arimidex group hadn’t had a recurrence after years versus 89.2% in the tamoxifen group. Fewer patients taking Arimidex died due to breast cancer compared with tamoxifen: eight deaths versus five with tamoxifen. As well, fewer patients taking Arimidex developed invasive breast cancer: 39 versus 63 in the tamoxifen group.

Younger women appeared to have a better response to Arimidex. The medication was effective in women younger than age 60, but not in women older than age 60.

Though patients who took Arimidex had a lower incidence of recurrence of early breast cancer, tamoxifen also helped reduce recurrence risk in the study. Based on these findings, patients with early breast cancer have two effective options for reducing risk of recurrence, with better chances of disease-free survival with Arimidex.

Reference: Margolese RG, Cecchini RS, Julian TB, et al. Primary results, NRG Oncology/NSABP B-35: A clinical trial of anastrozole (A) versus tamoxifen (tam) in postmenopausal patients with DCIS undergoing lumpectomy plus radiotherapy. Journal of Clinical Oncology. 33, 2015 (suppl; abstr LBA500).



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