Simple Summary: This retrospective study aims to classify a series of pituitary neuroendocrine tumours (PitNETs), typified according to the WHO 2017 recommendations, using Trouillas et al.’s clinicopathological classification from 2013. We analysed 166 patients who underwent PitNET surgery from 2013 to 2023. The tumours were identified according to the gene and immunohistochemistry expression of pituitary transcription factors and adenohypophyseal hormones. The PitNETs were graded based on the invasion observed in MRI and the Ki-67 index. The study found that grade 2a and 2b tumours, T2 signal intensity ratio (SIR), and silent corticotroph tumours were associated with lower progression-free survival rates. Tumour volume and T2 SIR were independent predictors of recurrence/progression, with a T2 SIR of 2 or more showing a significantly higher risk. These findings emphasise the prognostic value of the five-grade classification and underscore the importance of radiological evaluation for managing PitNETs. Abstract: Immunostaining of transcription factors allows a more exact classification of pituitary neuroendocrine tumours (PitNETs), but not a better prediction of their clinical behaviour. This retrospective, single-centre study aims to classify a series of PitNETs using Trouillas et al.’s clinicopathological classification from 2013. We analysed 166 patients undergoing PitNET surgery in 2013–2023. Tumours were identified according to the gene and immunohistochemical expression of PitNET transcription factors plus adenohypophyseal hormones. Tumours were classified according to a grading system based on MRI invasion and Ki-67 index. Eighty-one (48.8%) patients had grade 2a tumours; 71 (42.8%), grade 1a; 8 (4.8%), 2b; and 6 (3.6%), 1b. At a mean follow-up of 57.8 (standard deviation 30) months, 13.9% (n=23) showed recurrence/progression; independent predictors of recurrence were tumour volume (p=0.031) and T2 signal intensity ratio (SIR) (p<0.001). This risk was 18.6-fold higher for a T2 SIR of 2 or more. Grade 2a and 2b tumours, T2 SIR, and silent corticotroph adenomas (SCAs) were associated with lower progression-free survival. Our results add more evidence to the prognostic value of the five-grade PitNET classification and suggest higher clinical surveillance of patients with SCAs is warranted. The MRI findings highlight the increasing value of radiological evaluation for managing PitNETs.

Funding: PI21/01012. INSTITUTO DE SALUD CARLOS III. 2022