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Until the Women's Health Initiative Study, there was no consensus on the effects of exogenous estrogen in combination with a progestin, on breast cancer risk in postmenopausal women. However, this large prospective randomized trial has demonstrated the potentially harmful effects of hormone therapy (HT) on the risk of breast cancer w1x. Although there are studies that have demonstrated an association between increased density and increased risk of breast cancer, debates still continue in this area w2x. Our aim was to evaluate the effects of different types of hormone therapy on mammographic density.We examined 171 postmenopausal women; 102 women who started HT or estrogen therapy (ET) after the first mammographic examination, 22 women who had received tibolone (Livial ; Orga-᭨ non), 47 women who had not received any form of hormone therapy (control group). Patients who had received any form of hormone therapy within the last 3 months prior to the study were excluded as were those with hypertension, hyperlipidemia, type I or II diabetes mellitus, or existence of any previous breast neoplasm, or a family history of breast neoplasia. 27 women were on ET (10 patients were using 0.625 mg of conjugated equine estrogen (CEE), Premarin ; (Wyeth), 17 patients ᭨ were using 2 mg of 17 beta estradiol, Estrofem ; ᭨ (Novo Nordisk). 75 women were using continuous combined HT (27 patients were using 2 mg of 17 beta estradiol and 1 mg of norethisterone acetate (NETA) in one tablet daily, Kliogest ; (Novo ᭨ Nordisk), and 48 patients were using 0.625 mg of CEE and 2.5 mg medroxyprogesterone acetate (MPA) in one tablet daily, Premelle ; (Wyeth). ᭨ All the women reported continuous use of therapy. Mediolateral oblique and craniocaudal view mammograms were obtained by using high-resolution screen-film equipment (Mammomat-300; Siemens, Erlangen, Germany) and both breasts were examined. Two radiologists who were blinded to treatments, without any information about which mammograms were taken first evaluated the mammograms. We subjectively classified the degree of increase in mammographic density as follows: a 10-25% increase in parenchymal density was considered a minimal change, 26-50% was considered a moderate change and 50% or greater was

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