Endocrine Abstracts

Classification of pituitary neuroendocrine tumours (NETs) or pituitary adenomas is based on the expression of the anterior lobe pituitary hormones (FSH, LH, GH, Prolactin, TSH, ACTH and alpha-subunit of the glycoprotein hormones). Assessment of the transcription factors SF-1, Pit-1 and T-Pit has been a complement to the classification. Tumours negative for both pituitary hormones and transcription factors have been designated as null-cell adenomas. However, lack of sensitive and specific antibodies towards T-Pit has presented difficulties for the inclusion of these transcription factors into the classification system of pituitary endocrine tumours. Here, we present a novel purified polyclonal antibody (HPA072686) towards T-Pit and demonstrate its high sensitivity and specificity for immunohistochemistry-based identification of the cells with corticotroph differentiation. In an immunohistochemical study of a large cohort of pituitary adenomas of different types from 246 patients, a distinct nuclear expression of T-Pit was demonstrated in all ACTH-immunolabelled tumours, silent and clinically functioning, as well as in a proportion of tumours previously diagnosed as null-cell adenomas. None of the tumours that were immunoreactive for Pit-1, SF-1 or pituitary hormones, other than ACTH, expressed T-Pit. We expect that the availability of a reliable T-Pit antibody as a marker of corticotroph cell differentiation will contribute to: i) more precise classification of pituitary neuroendocrine tumours, particularly, those with sparse or no hormone expression, ii) better identification of silent corticotroph tumours that may have more aggressive clinical behaviour than silent gonadotroph tumours, and which are at the moment difficult to identify in cases with sparse or no ACTH expression, iii) more cost effective immunohistochemical screening of pituitary tumours based primarily on the use of the three transcription factors and iv) identification of potential corticotroph cell differentiation in non-pituitary NETs.