Pituitary tumours comprise a pathologically diverse group of neoplasms and exhibit a wide spectrum of clinical behaviour. Although generally benign, a subset demonstrates clinically “aggressive behaviour” (10-15%) and more rarely progress to develop distant metastatic disease (0.1-0.2%). Pathological classification has evolved over the past few decades, continuing to approximate improving understanding of tumour biology. The 2017 WHO heralded a paradigm shift, with tumours now classified according to cellular lineage, ascertained by transcription factor and hormonal immunohistochemistry. Prognostic value of Ki67 and mitotic count were retained, along with recognition of new “higher risk” histological types. However, the individual and additive prognostic value of these factors remained to be determined. The recent WHO 2022 classification, which controversially has rebranded pituitary adenomas as pituitary neuroendocrine tumours (PitNETs), incorporates further refinement of lineage-based classification, notably with identification of a new “plurihormonal” type, characterised by expression of multiple lineage transcription factors within a monomorphous population of cells. Streamlined processes are required for diagnostic reproducibility and economic feasibility, in order for recent research advances to be translated into clinically meaningful impacts.