Silent somatotroph tumour revisited from a study of 80 patients with and without acromegaly and a review of the literature

Silent somatotroph tumours are growth hormone (GH) immunoreactive (IR) pituitary tumours without clinical and biological signs of acromegaly. Their better characterisation is required to improve the diagnosis.Twenty-one silent somatotroph tumours were compared to 59 somatotroph tumours with acromegaly. Tumours in each group were classified into GH and plurihormonal (GH/prolactin (PRL)/±thyroid-stimulating hormone (TSH)) and into densely granulated (DG) and sparsely granulated (SG) types. The two groups were then compared with regards to proliferation (Ki-67, p53 indexes and mitotic count), differentiation (expression of somatostatin receptors SSTR2A-SSTR5 and transcription factor Pit-1) and secretory activity (% of GH- and PRL-IR cells).The silent somatotroph tumours represented 2% of all tested pituitary tumours combined. They were more frequent in women than in men (P = 0.002), more frequently plurihormonal and SG (P < 0.01), with a lower percentage of GH-IR cells (P < 0.0001) compared to those with acromegaly. They all expressed SSTR2A, SSTR5 and Pit-1. The plurihormonal (GH/PRL/±TSH) tumours were mostly observed in women (sex ratio: 3/1) and in patients who were generally younger than those with acromegaly (P < 0.001). They were larger (P < 0.001) with a higher Ki-67 index (P = 0.007).The silent somatotroph tumours are not uncommon. Their pathological diagnosis requires the immunodetection of GH and Pit-1. They are more frequently plurihormonal and more proliferative than those with acromegaly. A low secretory activity of these tumours might explain the normal plasma values for GH and insulin-like growth factor 1 (IGF1) and the absence of clinical signs of acromegaly.