Pituitary tumours without distinct lineage differentiation express stem cell marker SOX2.

CONTEXT: The recent WHO 2022 Classification of pituitary tumours identified a novel group of 'plurihormonal tumours without distinct lineage differentiation (WDLD)'. By definition, these express multiple combinations of lineage commitment transcription factors, in a monomorphous population of cells. OBJECTIVES: To determine the expression of stem cell markers (SOX2, Nestin, CD133) within tumours WDLD, immature PIT-1 lineage and acidophil stem cell tumours, compared with committed cell lineage tumours. METHODS: Retrospective evaluation of surgically resected pituitary tumours from St Vincent's Hospital, Sydney. Patients were selected to cover a range of tumour types, based on transcription factor and hormone immunohistochemistry. Clinical data was collected from patient files. Radiology reports were reviewed for size and invasion. Samples were analysed by immunohistochemistry and RT-qPCR for SF-1, PIT-1, T-PIT, SOX2, Nestin and CD133. Stem cell markers were compared between tumours WDLD and those with classically "mature" types. RESULTS: On immunohistochemistry, SOX2 was positive in a higher proportion of tumours WDLD compared with those meeting WHO lineage criteria, 7/10 v 10/42 (70 v 23.4%, p = 0.005). CD133 was positive in 2/10 tumours WDLD but 0/41 meeting lineage criteria, P = 0.003. On RT-qPCR, there was no significant difference in relative expression of stem cell markers (SOX2, CD133, Nestin) between tumours with and WDLD. CONCLUSIONS: Our study is the first to biologically characterise pituitary tumours WDLD. We demonstrate that these tumours exhibit a higher expression of the stem cell marker SOX2 compared with other lineage-differentiated tumours, suggesting possible involvement of stem cells in their development.

The evolution in pituitary tumour classification: a clinical perspective.

Objective: Pituitary tumours comprise a pathologically and clinically diverse group of neoplasms. Classification frameworks have changed dramatically in the past two decades, reflecting improving understanding of tumour biology. This narrative review examines the evolution of pituitary tumour classification, from a clinical perspective. Results: In 2004, pituitary tumours were classified as 'typical' or 'atypical', based on the presence of markers of proliferation, Ki67, mitotic count and p53. In 2017, the new WHO marked a major paradigm shift, with a new focus on lineage-based classification, determined by transcription factor and hormonal immunohistochemistry. The terms 'typical' and 'atypical' were omitted, though the importance of proliferative markers Ki67 and mitotic count was acknowledged. The recent WHO 2022 classification incorporates further refinements, specifically recognising some less common types that may represent less well-differentiated tumours. Whilst 'high risk' tumour types have been identified, further work is still required to improve prognostication. Conclusions: Recent WHO classifications have marked significant progress in the diagnostic evaluation of pituitary tumours, though shortcomings and challenges remain for both clinicians and pathologists in managing these tumours.

Predictors of pituitary tumour behaviour: an analysis from long-term follow-up in 2 tertiary centres.

OBJECTIVES: To determine the clinical utility of assessment of tumour invasion, markers of proliferation, and the French clinicopathological classification in pituitary tumour prognostication. METHODS: This is a retrospective evaluation of adult patients undergoing pituitary surgery at Oxford University and St Vincent's Hospitals, between 1989 and 2016, with at least 12 months of clinical data. Invasion was assessed radiologically, proliferative markers (Ki67, mitotic count, p53) by immunohistochemistry. Tumours were graded according to the clinicopathological classification. Intra- and interlaboratory variability of histopathology reporting was evaluated. OUTCOMES: (1) Tumour recurrence (radiological or reintervention ≥12 months postoperatively) and/or (2) "aggressive behaviour" (≥4 interventions and/or invasive tumour with recurrence/reintervention between 12 and 24 months postoperatively). RESULTS: A total of 386 patients were included, age at surgery was 56 (interquartile range [IQR] 41-67) years, 54% were male, and median follow-up was 90 months (range 44-126). Tumours were predominantly clinically nonfunctioning (252, 65%), with overall 53% invasive, and 10% that demonstrated ≥2 proliferative marker positivity. Recurrence was predicted by invasiveness (hazards ratio [HR] 1.6 [1.10-2.37], P .02), elevated mitotic count (HR 2.17 [1.21-3.89], P .01), grade (2b vs 1a HR 2.32 [1.06-5.03], P .03), and absence of gross total resection (HR 3.70 [1.72-8.00], P .01). Clinically defined aggressiveness was associated with elevated Ki67, mitotic count, and invasiveness. Ki67 reporting methodologies showed moderate correlation across laboratories (Phi 0.620), whereas p53 reporting reproducibility was poor (Phi 0.146). CONCLUSIONS: Proliferative markers, including Ki67 and mitotic count, but not p53, are important in predicting the development of aggressive pituitary tumour behaviour.

Pituitary tumours: molecular and genetic aspects.

'Pituitary tumours' is an umbrella term for various tumours originating from different regions of the hypothalamic-pituitary system. The vast majority of pituitary tumours are pituitary adenomas, also recently referred to as pituitary neuroendocrine tumours. The prevalence of clinically relevant pituitary adenomas is approximately 1 in 1000; other pituitary tumours such as craniopharyngioma and pituicytoma are comparatively very rare. This review addresses the molecular and genetic aspects of pituitary adenomas. We first discuss the germline genetic variants underlying familial pituitary tumours, which account for approximately 5% of all pituitary adenoma cases. This includes variants in established pituitary adenoma/hyperplasia predisposition genes (MEN1, PRKAR1A, AIP, CDKN1B, GPR101, SDHA, SDHB, SDHC, SDHD, SDHAF2) as well as emerging genetic associations. In addition, we discuss McCune-Albright syndrome which lies between the germline and somatic pituitary tumour genes as the causative GNAS mutations are postzygotic rather than being inherited, and the condition is associated with multiglandular features due to the involvement of different cell lines rather than being limited to the pituitary. By contrast, somatic GNAS mutations contribute to sporadic acromegaly. USP8 is the only other gene where somatic driver mutations have been established in sporadic pituitary tumorigenesis. However, there are now known to be a variety of other somatic genetic and molecular changes underpinning sporadic pituitary adenomas which we review here, namely: copy number variation, molecular changes in signalling and hypoxia pathways, epithelial-mesenchymal transition, DNA repair, senescence, the immune microenvironment and epigenetics.

Transcription factor immunohistochemistry in the diagnosis of pituitary tumours.

OBJECTIVE: The clinical utility and prognostic value of WHO 2017 lineage-based classification of pituitary tumours have not been assessed. This study aimed to (1) determine the clinical utility of transcription factor analysis for classification of pituitary tumours and (2) determine the prognostic value of improved lineage-based classification of pituitary tumours. METHODS: This was a retrospective evaluation of patients who underwent surgical resection of pituitary tumours at St Vincent's Public and Private Hospitals, Sydney, Australia between 1990 and 2016. Included patients were at least 18 years of age and had complete histopathological data, forming the 'histological cohort'. Patients with at least 12 months of post-surgical follow-up were included in the subgroup 'clinical cohort'. The diagnostic efficacy of transcription factor immunohistochemistry in conjunction with hormone immunohistochemistry was compared with hormone immunohistochemistry alone. The prognostic value of identifying 'higher-risk' histological subtypes was assessed. RESULTS: There were 171 patient tumour samples analyzed in the histological cohort. Of these, there were 95 patients forming the clinical cohort. Subtype diagnosis was changed in 20/171 (12%) of tumours. Within the clinical cohort, there were 21/95 (22%) patients identified with higher-risk histological subtype tumours. These were associated with tumour invasiveness (P = 0.050), early recurrence (12-24 months, P = 0.013), shorter median time to recurrence (49 (IQR: 22.5-73.0) vs 15 (IQR: 12.0-25.0) months, P = 0.005) and reduced recurrence-free survival (P = 0.031). CONCLUSIONS: Application of transcription factor analysis, in addition to hormone immunohistochemistry, allows for refined pituitary tumour classification and may facilitate an improved approach to prognostication.

Towards precision medicine for clinically non-functioning pituitary tumours.

OBJECTIVE: Clinically non-functioning pituitary tumours (NFPT) are a heterogenous group of neoplasms with diverse outcomes. The purpose of this narrative review was to summarize available data on predictive factors, both in routine practice and research settings. DESIGN: A literature review was conducted for papers published in peer-reviewed journals, investigating clinical, radiological, pathological and genetic predictive factors in NFPT. RESULTS: Several clinical and radiological factors have been associated with NFPT recurrence and/or aggressiveness, including larger size and pre-/post-operative growth rates. Application of transcription factor immunohistochemistry has given rise to improved subtype identification, including 'higher-risk' subtypes, in routine clinical practice. Numerous other pathological and genetic biomarkers have demonstrated promise for prognostication in the research setting. CONCLUSION: NFPT are a heterogenous group of tumours, characterized by diverse presentation, pathogenesis and outcomes. Ongoing refinements in understanding of tumour biology are likely to pave the way to improved integrative prognostication and precision medicine for NFPT.