Tamoxifen in patients with dopamine agonist-resistant prolactinomas

Aim — to assess the efficacy and safety of tamoxifen in patients with prolactin-secreting pituitary tumors resistant to treatment with dopamine agonists.

Material and methods. The study included 6 females aged 23—38 years. All patients received cabergoline for a prolonged time without normalization of prolactin levels and reversal of secondary hypogonadism. The cabergoline dose was 1—7 mg/week. Cabergoline administration was combined with tamoxifen at a dose of 20 mg per day, with a subsequent increase to 40 mg per day after 4 weeks of treatment. Patients received this combination therapy for 3 months.

Results. Combined cabergoline and tamoxifen therapy resulted in a significant reduction in prolactin levels in all treated patients, which amounted to 22—66% of the baseline value. However, none of the patients achieved complete normalization of prolactin levels. Despite this fact, 2 patients developed normalization of the menstrual cycle. One of these got pregnant 1.5 months after discontinuation of tamoxifen and gave birth to a child. The second patient had amenorrhea recurrence after tamoxifen discontinuation. After tamoxifen discontinuation, two patients with amenorrhea were treated with dydrogesterone to prevent endometrial hyperplasia. One patient who had a normal menstrual function before tamoxifen developed endometrial hyperplasia, which was the cause for separate diagnostic curettage and a reduction in the tamoxifen dose to 20 mg per day. One month after tamoxifen discontinuation, the patient naturally conceived and subsequently gave birth to twins. One patient underwent placement of an intrauterine system containing levonorgestrel 2 months before the start of tamoxifen.

Conclusion. Tamoxifen in combination with cabergoline provides an additional decrease in prolactin levels in patients with initial resistance to dopamine agonists. In patients with dopamine agonist-resistant prolactinomas and hypoestrogenemia, tamoxifen leads to normalization of the menstrual cycle.

prolactinoma, dopamine agonist resistance, tamoxifen

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