SAT-075 - Serum Luteinizing Hormone/Follicle-Stimulating Hormone Do Not Reliably Predict Tumor Volume in Functioning Gonadotropin-Secreting Pituitary Adenomas: A Single-Center Series of 81 Patients (1988-2022)

Introduction: Functioning gonadotropin-secreting pituitary adenomas are rare. True “functioning” gonadotropinomas; defined by immunohistochemical positivity for LH and/or FSH together with elevated serum LH and/or FSH; are infrequently reported and typically described only in case reports or small series. We evaluated whether serum gonadotropin levels correlate with tumor volume in the largest single-center cohort to date.
Patients and

Methods: We retrospectively analyzed 81 patients with functioning gonadotropinomas treated at one institution (1988 – 2022). Inclusion required immunohistochemical positivity for LH and/or FSH and elevated serum LH and/or FSH. Tumor volume was derived from preoperative imaging. Tumors were categorized as microadenomas ( < 10 mm), macroadenomas (≥ 10 mm and < 40 mm), or giant adenomas (≥40 mm in at least one plane). Group comparisons used two-sided t-tests with unequal variances; correlations were assessed using log-transformed serum values and log tumor volume.

Results: Gonadotropinomas accounted for 2.3% of the overall analysed cohort with n = 81; 61 women and 20 men. Microadenomas were rare (n = 2), whereas most tumors were macroadenomas (n = 73) and 6 giant adenomas. Mean serum LH and FSH in the full cohort were 13.59 ± 10.26 mU/ml (LH) and 39.55 ± 22.68 mU/ml (FSH), respectively, with mean tumor volume 10157 ± 30743 mm³, indicating marked variability. LH levels differed by sex (women 15.28 ± 10.41 vs men 8.60 ±8.19 mU/ml; p = 0.008), while FSH showed only a trend (p = 0.073). FSH was significantly different between primary operations and reoperations (p < 0.001), whereas LH did not differ (p = 0.964). In correlation analyses (n = 79 due to missing hormone values), no significant association was found between tumor volume and raw LH (r = -0.033; p = 0.77) or raw FSH (r = 0.009; p = 0.93). A weak inverse correlation was observed for log(LH) versus log(volume) (r = -0.259; p = 0.021), but this relationship was attenuated after accounting for sex, consistent with sex-related differences in both tumor volume and LH secretion. Tumor volume was significantly associated with invasiveness (p < 0.001) and differed by sex (p = 0.002), while age was not associated with tumor volume (p= 0.82).

Conclusion: In this large single-center series of functioning gonadotropinomas, serum LH and FSH levels showed extreme variability and did not provide a reliable estimate of tumor volume. Any apparent inverse association between LH secretion and tumor volume was confounded by sex-related differences. These findings emphasize that serum gonadotropins have limited value for predicting tumor burden or for longitudinal monitoring, and that imaging, together with assessment of invasiveness, remains central for diagnosis and follow-up in this rare tumor entity.
This study was supported by a grant of the Förderverein Neurochirurgische Forschung an der Universität Erlangen-Nürnberg e.V.

*Unless otherwise noted, all abstracts presented at ENDO must not be released to the press or the public until the date and time of presentation. For oral presentations, the abstracts are embargoed until the session begins. The Endocrine Society reserves the right to lift the embargo on specific abstracts that are selected for promotion prior to or during ENDO.*