FRI319 Diagnostic And Management Challenges In A Patient With A Giant Pituitary Lactosomatotroph Adenoma

Disclosure: C.R. Peixe: None. D. López-Presa: None. M. Bugalho: None. P. Marques: None. Introduction: Giant prolactinomas are rare, accounting for only 2–3% of all prolactinomas. Although benign, several challenges may emerge at diagnosis and during their management. Case: A 38-yr man was incidentally diagnosed with a large skull base tumor on CT-scan undertaken due to head trauma. MRI showed a 55x33mm skull base mass, involving the clivus and sellar/parasellar regions, with bilateral cavernous sinus invasion. A chordoma was suspected leading to a transnasal biopsy, which revealed a PIT1+-plurihormonal pituitary adenoma. His serum prolactin levels were then assessed, which were markedly elevated at 50,414ng/mL (NR:4-15), with concomitant raised IGF-1 at 323ng/mL (NR:101-221). He was then referred to our Endocrine department. Retrospectively, there was a 3-yr history of erectile dysfunction, decreased libido, and infertility, although his testosterone levels were within reference range (307ng/dL; NR:240-830), and sperm analysis parameters were normal. He commenced on low dose cabergoline (0.5mg/week) and two months later clinical improvement was noted, accompanied by a marked reduction of prolactin (830ng/mL) and tumor shrinkage. He remains on cabergoline for ten months, and his latest prolactin and IGF-1 levels were, respectively, 496 and 224ng/mL. In the light of patient’s normal spermogram and restored sexual function, the couple has been referred to the Fertility clinic. Conclusions: The differential diagnosis of large skull base tumors, particularly those affecting sellar/clival regions, must always include prolactinoma, hence serum prolactin should be measured keeping in mind the possible occurrence of hook effect. Most giant prolactinomas respond to dopamine agonists, which should be considered as a first-line therapy, with marked reductions in both prolactin and tumor size often seen within the first weeks of treatment. GH-cosecretion may also ameliorate/normalize with dopamine agonists. In prolactinoma patients, infertility may or may not be directly related with hyperprolactinemia, hence a careful assessment is required, and its management may imply assisted reproductive techniques. Presentation: Friday, June 16, 2023