Many breast tumours are dependent on the female hormone, oestrogen, for their continued growth. Tamoxifen and anastrozole are both hormonal treatments but they work differently. Tamoxifen prevents breast cancer cells from picking up oestrogen. Anastrozole, one of a group of drugs known as aromatase inhibitors, acts differently by blocking the natural production of oestrogen in postmenopausal women.

Anastrozole has fewer serious side effects than tamoxifen, which can cause womb cancer and blood clots. However, anastrozole has some side effects such as hot flushes, vaginal bleeding and an increased risk of osteoporosis.

Many experts believe that hormonal treatments can prevent breast cancer from returning in women who have had DCIS, either in the same DCIS breast or in the opposite breast. But there is still uncertainty as to which of these treatments is best.

Research has shown that tamoxifen reduces the risk of the disease in women with DCIS¹. However, Anastrozole may be a better treatment for these women because it has already been proven to be more effective than tamoxifen at reducing disease recurrence in women with early invasive breast cancer².

1. Bryant J, Land S, Allred C, Paik S, Dignam J, Habel L, Smith R, Geyer C, Fisher E, Fisher B, Wolmark N. DCIS: Evidence From Randomized Trials, 8th International Conference on Adjuvant Therapy of Primary Breast Cancer, St. Gallen Switzerland, Mar 12-15, 2003 (invited presentation).
2. ATAC Trialists' Group. Results of the ATAC (Arimidex, Tamoxifen, Alone or in Combination) trial after completion of 5 years' adjuvant treatment for breast cancer. Lancet 2005, 365 (9453): 60-62.