SAT-260 Resolution of a Cystic Macroprolactinoma with Dopamine Agonist Therapy

Background. Prolactinomas with cystic regions occupying ≥ 50% of tumor volume are classified as cystic prolactinomas. They appear to arise from tumor necrosis or hemorrhage. Though Pituitary Society guidelines recommend surgery as first-line treatment for cystic prolactinomas, there is evidence that cystic prolactinomas are hormonally and anatomically responsive to treatment with dopamine agonists (DA). We present a case of a cystic macroprolactinoma fully responding to treatment with cabergoline. Case. A 31 year old male was referred for evaluation of gynecomastia, diminished libido, and erectile dysfunction that occurred over the course of eight months. Bilateral glandular breast tissue with a slight right asymmetry was present. Testes were 15–20 mL, soft, and without masses. Phallus and pubic hair were unremarkable. Morning (8 AM) testosterone, estradiol, and LH levels were 92 ng/dL (348–1197), 13.4 pg/mL (7.6–42.6), and 2.0 mIU/mL (1.7–8.6), respectively. Prolactin level was 331 ng/mL (4–15), and MRI with pituitary protocol revealed a 1.4 x 1.0 x 1.5 cm cystic mass with peripheral rim enhancement and extension into the suprasellar cistern. No mass effect on the optic chiasm was observed. Somatotroph, thyrotroph, and corticotroph axes were unaffected. Cystic macroprolactinoma causing hyponadotropic hypogonadism complicated by gynecomastia was diagnosed. The patient chose initial management with cabergoline 0.25 mg twice weekly. Three months after starting treatment, libido and erectile function had recovered to baseline, 8 AM testosterone was 607 ng/dL, and hyperprolactinemia was well controlled (4.2 ng/mL). At six months, anatomic resolution of the cystic macroprolactinoma was demonstrated on repeat pituitary MRI. Plastic surgery was required for management of gynecomastia. Conclusions. Surgery is recommended for management of cystic prolactinomas due to concern that a lack of dopamine receptors in the cystic components of tumors will make DA ineffective reducing tumor size. However, this case joins a growing body of evidence that DA can treat hyperprolactinemia and induce regression of cystic macroprolactinomas. For example, in a retrospective case review of patients with cystic macroprolactinomas at Massachusetts General Hospital, persistent cyst reduction occurred in 20 of 22 patients treated initially with DA, and median reduction in cyst volume exceeded 80 percent. Median time to documented cyst reduction was approximately six months, and there was no difference in degree of cyst reduction for patients treated with bromocriptine or cabergoline. The response of cystic prolactinomas to DA is similar to solid prolactinomas, and DA are reasonable initial treatment for cystic macroprolactinomas without clear indications for surgery.