Use of transvaginal ultrasonography to monitor the effects of tamoxifen on uterine leiomyoma size and ovarian cyst formation.

To evaluate the effects of tamoxifen on leiomyomas and ovarian cysts in postmenopausal breast cancer patients, uterine and leiomyoma volumes were monitored sonographically in 17 postmenopausal women receiving postoperative tamoxifen for breast cancer; patients were examined twice with a mean of 1.18 +/- 0.17 years between examinations. The mean increase in leiomyoma volume was 1.26 +/- 0.73 cm3. The mean myoma volume was significantly larger at follow-up evaluation than at initial ultrasonography (5.75 +/- 1.09 cm3 versus 4.36 +/- 0.817 cm3, respectively; Wilcoxon signed rank test, P = 0.0218). Six women developed new leiomyomas. Of the 21 leiomyomas initially detected, 13 increased, six decreased, and two were unchanged in volume. The mean increase in uterine volume was 17.45 +/- 8.49 cm3. Three patients had simple ovarian cysts at initial ultrasonographic examination, two of which remained unchanged in size, and the third resolved. Two patients had newly developed simple ovarian cysts. The increase in uterine and leiomyoma volumes with the development of new leiomyomas and the persistence or development of ovarian cysts in some patients support the existence of agonistic tamoxifen effects. Serial measurements of uterine and leiomyoma volumes and surveillance for ovarian cysts is recommended for tamoxifen users.