SUN-049 The correlation between tumor size and hormonal oversecretion in functioning pituitary adenomas

Abstract Disclosure: H. Külper: None. Y. Zhao: None. A. Mattson: None. M. Buchfelder: None. Introduction: Hormone secretion from functioning pituitary adenomas depends on several factors, such as the secretory potential of the neoplasm and regressive changes within the adenoma. Also, a dependency on tumor size has been suggested. In this study, we compared tumor size and oversecretion of respective hormones in a large, prospectively documented series of all types of secreting pituitary adenomas treated between 1988 and 2022. Patients and Methods: All 3496 patients were operated in our institution. Tumour size was determined by analysis of preoperative imaging and intraoperative comparison with surgical instruments. Hormones were measured with commercially available RIA or ELISA methods. The tumors were classified based on immunohistochemistry and hormonal laboratory results. The final classification were prolactinomas (n=848), acromegaly and gigantism (n=1492), Cushing’s disease (n=950), Nelson’s syndrome (n=65), TSHomas (n=60) and gonadotropinomas (n=81). Results were expressed as mean levels ± SD. Tumour size was classified into microadenomas (estimated diameter < 10 mm), macroadenomas (≥10 mm and <40 mm) whereas giant adenomas required an estimated tumour diameter of 40 mm at least in one plane. Results: A positive size-oversecretion relationship was found in prolactinomas (r=0.436) and acromegaly (r=0.0496). The mean prolactin level in prolactinomas was significantly lower in microadenomas (2997±2677 µU/ml) than in macroadenomas (34818±86634 µU/ml) and giant adenomas (237328±521030 µU/ml). Invasive tumours had higher levels (100328±292224 µU/ml) than enclosed ones (17723±68706 µU/ml). Likewise, growth hormone levels in acromegaly were significantly lower in microadenomas (13.7±36.7 ng/ml) than in macroadenomas (87.3±1627.4 ng/ml) and giant adenomas (137.9±319.7 ng/ml). Moreover, growth hormone was higher in invasive (165.8±2409 ng/ml) than in enclosed ones (26.3±44.5 ng/ml). In Cushing’s disease, ACTH plasma levels were 72.7±66.7 pg/ml in microadenomas, 104.5±111.8 pg/ml in macroadenomas and 148.9±93.5 pg/ml in giant adenomas with an r=0.21 for all tumors. However, no significant differences in tumor types were encountered in TSHomas (r=-0.006) and gonadotropinomas (LH: r=-0.26; FSH: r=-0.07). Discussion: Hormone secretion shows a extremely variable pattern as expressed by the enormous standard variations. Nevertheless, we can confirm with our accurrately determined high numbers of investigated tumours, that there is a reliable size-secretion correlation in prolactinomas, growth hormone secreting adenomas and also for ACTH secretion in Cushing‘s disease. This can be clinically useful to distinguish other causes of e.g. hyperprolactinaemia from secreting adenomas. However, we showed that also other factors than just the mere tumor diameter influence the magnitude of hormonal oversecretion. Presentation: Sunday, July 13, 2025