FRI322 Lack Of Tumor Size Change With Long-term Cabergoline For Prolactinoma

Abstract

Abstract Disclosure: S. Bendaram: None. V. Kantorovich: None. Introduction: Prolactinomas are the most common tumors of the pituitary gland and account for about 40% of all Pituitary adenomas, of which 10% are macroprolactinomas measuring >1 cm. Dopamine Agonists (DAs) normalize the prolactin levels and aid in shrinkage of the tumor size. We present two cases of Macroprolactinomas with biochemical response to DAs but no shrinkage in size as expected. Case 1: 75-year-old male with history of hypertension, left frontal MCA stroke with residual aphasia who underwent brain MRI for a recent TIA, was found to have a new 2.3 x 1.9 x 2.4 cm mass in the pituitary fossa invading the right cavernous sinus, concerning for a pituitary macroadenoma. Prolactin levels were 4152 ng/ml on dilution study, low testosterone with inappropriately normal LH/FSH. He denied any symptoms from compression, hyperprolactinemia or hypogonadism. After starting Cabergoline 0.25 mg biweekly, repeat levels in 2 weeks showed a decline in prolactin levels to 808.7 ng/ml. Visual Field (VF) testing was abnormal but was unreliable due to high fixation losses. Same dose of cabergoline was continued, with decline in prolactin further to 37.8 ng/ml, while a repeat MRI Brain showed no substantial change in the size of the mass. Cabergoline was doubled, and a repeat MRI still demonstrated same size of the mass, despite prolactin levels decreasing to below normal range. Case 2: 62-year-old male with history of macroprolactinoma for >3 years, but non-adherent to medications, who presented to his PCP with persistent occipital headaches, and was referred to Endocrinology due to repeat MRI brain revealing interval increase in the size of sellar and suprasellar mass measuring 2.2 x 2.2 x 2.9 cm in size consistent with macroadenoma with mass-effect on the optic chiasm and prechiasmatic optic nerves. Evaluation of pituitary panel revealed prolactin levels of 1352 ng/ml, low testosterone and LH, while the rest of the labs were normal. He was started on cabergoline 0.5 mg biweekly, and a repeat prolactin level after a single dose of cabergoline improved to 469 ng/ml. He was continued on the same dose with prolactin dropping to 2.6 ng/ml in 2 months, and further to 1.8 ng/dl after 10 months of treatment. Initial VF testing also demonstrated some degree of defect with compression of optic chiasm. Repeat MRI 3 months after initiation of cabergoline revealed interval decrease in size of macroadenoma to 2.1 cm in the largest dimension, which stayed the same on the recent imaging. Discussion: DAs like Cabergoline are first line therapy for prolactinomas. Fibrotic changes from long standing adenomas might be a possibility causing resistance to shrinkage of tumor, however it would be interesting to know if any specific molecular mechanisms that could be involved. In tumors with significant mass effect or those not responding to MT, Surgery is the preferred next step, and neurosurgery evaluation is necessary for further management. Presentation: Friday, June 16, 2023