This study is based on 194 patients with primary breast cancer treated with adjuvant CNF combination chemotherapy, who were followed-up for the risk of subsequent neoplasms. During an average follow-up of 4.8 years, 16 cases of new cancers were detected. Nine non-breast cancers were observed versus 2.2 expected (standardized incidence ratio 4.2). Of the patients with subsequent malignancies, 88% had received antiestrogen (chemohormonal adjuvant therapy); the percentage among all patients was 25%. We conclude that the benefit derived from adjuvant therapy of breast cancer may be reduced because of an increased risk of subsequent cancers.