SAT-478 Successful Management of an Atypical Prolactinoma with Radiotherapy

INTRODUCTION: Prolactinomas are the most common pituitary adenoma and are usually slow growing tumors with a good response to medical therapy with dopamine agonists. Atypical adenomas are a variant, defined by invasive growth, high Ki-67/MIB-1 proliferative index, and high p53. These tumors are often recurrent and difficult to treat with standard therapy and surgery. The objective of this case is highlight successful treatment of an atypical aggressive prolactinoma with radiotherapy. CASE: A 63 year-old male initially presented with rapid development of visual defects and headache. He was found to have a prolactin-secreting pituitary macrodenoma with upward displacement of the optic chiasm, and bitemporal hemianopsia on formal visual field testing. He underwent transphenoidal resection of the tumor. Despite treatment on cabergoline patient had increasing prolactin levels, peripheral vision loss, and recurrence on imaging requiring a second surgery. Pathology consistent with an atypical prolactinoma with increased nuclear pleomorphism (increased mitoses up to 2 mitoses/10 HPF), high proliferation labeling index using Ki67 (11%). Despite carbergoline (up to 8mg/week), prolactin continued to rise (>4700 ng/mL) and developed severe compression of the optic chiasm leading to a third surgical resection. He was initiated on pasireotide but within 6 weeks had continued growth of tumor. Adjunctive radiotherapy was decided to be the best option, as patient was resistant to further surgical interventions. Fractionated radiation therapy was given, opposed to stereotactic given the proximity to the optic apparatus. He completed radiation therapy with 5040 cGy and has had a marked response. His prolactin continues to trend down, MRI with interval decrease in size, and visual field testing with improvement clinically. CONCLUSION: This case highlights the aggressive nature of these tumors, and resistance to therapy. Labeling of Ki67 have been demonstrated to correspond with the rate of invasive growth, and aggressive behavior. Despite prolactinomas having previously been described as poor responders to fractionated radiation therapy with variable success rates, this is an option that should be considered in those who have failed multiple other treatment modalities.