Endocrine Abstracts

Background: Serum prolactin levels at presentation can be useful in distinguishing between non-functioning pituitary macroadenomas and prolactinomas in order to guide appropriate therapy. Although thresholds have been suggested to distinguish between the two tumour-types, there remains some debate regarding discriminatory levels.

Objective: To assess the baseline serum prolactin levels in a series of patients with histologically-proven non-functioning pituitary tumours and to correlate prolactin levels with size of tumour, which may reflect degree of stalk compression.

Methods: Patients presenting to the University Hospital of Wales, Cardiff, with non-functioning pituitary adenomas (histologically proven) between 2011–2019 were studied by examining biochemical, histological and radiological data.

Results: A total number of 210 patients with histologically-proven non-functioning pitutiary macroadenomas were identified (130 male, 80 female). The median age at surgery was 57 yrs (range 24–86 yrs). Median prolactin inthe total group was 408 mU/l (range 3–3390), males 321 mU/l (range 35–1581), females 656 mU/l (range 3–3390). 96/210 (45.7%) patients had a high prolactin. 24/96 (25%) of these patients were on medications that could cause a high prolactin. Median prolactin for patients on medications was 792 mU/l (range 443–3390). Median male prolactin on medications was 766 mU/l (range 443–1450) and in females 792 mU/l (range 618–1880). In the total group, 88.1% had serum prolactin <1000 mU/l and 99.0% <2000 mU/l. Of the 2 patients with prolactin >2000 mU/l, one was taking an oestrogen preparation for initial presumed polycyctic ovary syndrome. There was a negative correlation between tumour size and prolactin levels with Pearson’s correlation of –0.09 (P = 0.24). Those with tumour size <10 cm³ had mean prolactin 561 mU/l compared to 486 mU/l in those with tumours >10 cm³ (P = 0.3).

Conclusions: Our large data series supports previous evidence that serum prolactin is rarely >2000 mU/l in non-functioning pituitary adenomas. In these cases a trial of dopamine agonist therapy is warranted to see if there is any reduction in tumour size. Although a negative correlation between tumour size and serum prolactin was seen, this was not found to be statistically significant.