METHODS	4724 postmenopausal patients with unilateral invasive , oestrogen-receptor-positive or oestrogen-receptor-unknown breast cancer who were disease-free on 2-3 years of tamoxifen , were randomly assigned to switch to exemestane ( n = 2352 ) or to continue tamoxifen ( n = 2372 ) for the remainder of a 5-year endocrine treatment period .\