A randomised trial of letrozole in postmenopausal women after five years of tamoxifen therapy for early stage breast cancer. - Goss,P.E.; Ingle,J.N.; Martino,S.; Robert,N.J.; Muss,H.B.; Piccart,M.J.; Castiglione,M.; Tu,D.; Shepherd,L.E.; Pritchard,K.I. (N Engl J Med, 2003)