In 1987 a chemoprevention trial was started at the Istituto Nazionale Tumori of Milan to evaluate the efficacy of fenretinide or 4-HPR (an effective agent against carcinogen-induced epithelial tumours in experimental animals) in reducing the incidence of contralateral breast cancer in women previously treated for an early breast cancer (pT1, pT2, N-). Patients were randomised into two groups: 4-HPR 200 mg/day vs. no treatment. We reviewed the mammograms of 149 patients who received 4-HPR for at least 4 years to examine whether changes seen in the mammary glands of rats could also be seen in women. For each patient, at least five mammograms (one at baseline and four annual controls) of the contralateral breast were classified according to Wolfe's parenchymal patterns (N1, P1, P2, DY). With the daily dosage of 200 mg and after follow-up, no changes in mammographic patterns were observed.