THU078 The Definition And Epidemiology Of Giant Pituitary GH-Secreting Adenomas Based On Clinical, Imaging, And Hormonal Parameters: A Pilot Study

Disclosure: L.M. Del Corso: None. M.C. Silva: None. S.Z. Fidalski: None. C.L. Boguszewski: None. Acromegaly is a chronic disease, caused by a GH-secreting pituitary adenoma in most cases. At diagnosis, around 75% of patients have a macroadenoma, which constitute a heterogeneous group with variable biological behavior, therapeutic response, and prognosis. Giant adenomas (GA) have been defined as those which are more than 40 mm at their largest in diameter, but this is an arbitrary definition lacking comparative studies to investigate tumor size at diagnosis with clinical presentation, response to treatment and the evolution of acromegaly patients. Thus, the aim of our study was to compare the aforementioned variables according to the tumor size at diagnosis and review the diagnostic criteria for giant GH-secreting adenomas. In this observational, retrospective, single-centre pilot study, we have retrieved data from 161 medical records and evaluated age, sex, duration of symptoms, GH levels, presence of type 2 diabetes mellitus (T2DM), hypertension and hypopituitarism, imaging characteristics, and the need for adjuvant therapy with somatostatin receptor ligands (SRL) or other drugs. Study population was classified into four groups according to tumor size at diagnosis: (I) <10 mm (microadenomas; n=14); (II) 10-29 mm (n=84); (III) 30-39 mm (n=10); (IV) 40 mm or more (n=9). The final study group consisted of 117 individuals (49% men; mean age 43 ± 13 yrs). Hypopituitarism was significantly more frequent in groups III and IV compared to groups I and II (p=0.004), with no difference between groups III and IV (p=0,3). There was a higher proportion of invasive adenomas when the lesions ≥ 30 mm were compared to groups I and II (p=0.008), but with no difference between groups III and IV (p=0.62). Sixty percent of patients in group III (n=6) and 44% of patients in group IV (n=4) needed other drug therapy than SRL (cabergoline and/or pegvisomant), a higher proportion compared to those of groups I (n=1; 7%) and II (n=25; 30%) (p=0.04), again without difference between groups III and IV (p=0,7). Regarding the initial levels of GH, a significant difference was observed between groups I and IV (p=0.04), but this difference was not observed in the other groups. There were no statistical differences in relation to sex, duration of symptoms, need for SRL therapy, prevalence of hypertension and T2DM between study groups. Our study raises the hypothesis that giant adenomas should be defined as tumors larger than 30 mm, as the clinical behavior of tumors above this cutoff point seems to be similar in comparison with tumors larger than 40 mm but different from those of smaller sizes. Presentation: Thursday, June 15, 2023