Switching treatment to the drug anastrozole after two years of tamoxifen is beneficial for women with early breast cancer

Switching treatment to the drug anastrozole after two years of tamoxifen can improve eventfree survival for postmenopausal women with early breast cancer, concludes a study in this week’s issue of The Lancet.

For more than 20 years tamoxifen has been the standard treatment after surgery for postmenopausal women with hormone-responsive early breast cancer. However, research has shown that an aromatase inhibitor called anastrozole is effective and tolerable in this group of patients compared with tamoxifen when used as a first-line treatment. Studies have also suggested that taking anastrozole after two years of tamoxifen could be beneficial.

Raimund Jakesz (Vienna Medical University, Vienna, Austria) and colleagues from the Austrian Breast and Colorectal Cancer Study Group and the German Adjuvant Breast Cancer Group combined data from two multicentre, randomised trials looking at the effect of taking anastrozole after tamoxifen. In both trials postmenopausal women who had received two years of tamoxifen treatment were randomised to receive anastrozole (1618 women) or tamoxifen (1606 women) for a further three years. The investigators found that after two years of follow-up there was a 40% decrease in the risk of an event for women in the anastrozole group when compared with women on tamoxifen (67 events with anastrozole vs 110 with tamoxifen). The researchers defined an event as a local or distant recurrence, or cancer arising in the other breast. More patients had bone fractures on anastrozole but there were fewer cases of blood clots than in the tamoxifen group.

Professor Jakesz concludes: “Although further investigation is necessary to ascertain the ideal sequence and duration of adjuvant endocrine therapy, this combined analysis confirms that post-menopausal women who receive tamoxifen as adjuvant therapy should be switched to anastrozole after 2 years of treatment.”

In an accompanying Comment Anthony Howell (Christie Hospital NHS Trust, Manchester, UK) states: “The aromatase inhibitors show superiority over tamoxifen when used immediately after surgery (anastrozole, letrozole) or after 2–3 years of tamoxifen (anastrozole, exemestane). Letrozole and anastrozole also show superiorly over placebo when given after 5 years of tamoxifen.”