DNA Methylation Pattern in Somatotroph Pituitary Neuroendocrine Tumors

Reassessment of Plurihormonal Pituitary Adenomas/PitNETs

Plurihormonal pituitary adenomas/neuroendocrine tumors express multiple pituitary hormones and/or transcription factors, as determined by immunohistochemistry (IHC). Three types exist based on Endocrine WHO 2022 classification: mature plurihormonal PIT1 (pituitary-specific POU-class homeodomain factor-1), immature PIT1-lineage tumors, and a third type with unusual combinations of pituitary hormones and/or transcription factors. However, since then, "somatogonatotroph"/"multilineage" tumors with PIT1/SF1 (steroidogenic factor 1) co-expression have been described, possibly confounding this classification. We performed a database search, from 2018 to 2023, to identify and reclassify tumors, correlating with neuroimaging and endocrinological features at presentation. We identified 22 cases: M 9:F 13, mean age at surgery 51±16 years. The most common symptoms at initial presentation were headaches and/or vision changes (6/22) and acromegaly (5/22). All tumors were macroadenomas, mean diameter of 25±17mm; 11/22 (50%) had cavernous sinus invasion. More than 70% of tumors clinically secreted at least 1 hormone, and 27% tumors secreted at least 2 different hormones. Four patients underwent >1 surgical intervention. Reclassification by IHC yielded almost exclusively 2 types: immature PIT1-lineage (9/22) and "somatogonadotroph"/"multilineage tumors" with PIT1/SF1 co-expression (12/22), the latter replacing mature plurihormonal tumors. One true unusual plurihormonal tumor was identified. The extent of growth hormone, prolactin, thyroid stimulating hormone, PIT1, and SF1 IHC was variable, but immunopositivity for follicle-stimulating hormone and/or luteinizing hormone was nearly confined to co-expressors, distinguishing these from immature PIT1-lineage tumors. In conclusion, tumor size, invasiveness, and endocrinopathies do not distinguish PIT1/SF1 co-expressing tumors from immature PIT1-lineage tumors preoperatively; only full IHC pituitary workup allows distinction.

Pituitary neuroendocrine tumors with PIT1/SF1 co-expression show distinct clinicopathological and molecular features

Pituitary neuroendocrine tumors (PitNETs) are classified according to cell lineage, which requires immunohistochemistry for adenohypophyseal hormones and the transcription factors (TFs) PIT1, SF1, and TPIT. According to the current WHO 2022 classification, PitNETs with co-expression of multiple TFs are termed "plurihormonal". Previously, PIT1/SF1 co-expression was prevailingly reported in PitNETs, which otherwise correspond to the somatotroph lineage. However, little is known about such tumors and the WHO classification has not recognized their significance. We compiled an in-house case series of 100 tumors, previously diagnosed as somatotroph PitNETs. Following TF staining, histopathological features associated with PIT1/SF1 co-expression were assessed. Integration of in-house and publicly available sample data allowed for a meta-analysis of SF1-associated clinicopathological and molecular features across a total of 270 somatotroph PitNETs. The majority (74%, 52/70) of our densely granulated somatotroph PitNETs (DGST) unequivocally co-expressed PIT1 and SF1 (DGST-PIT1/SF1). None (0%, 0/30) of our sparsely granulated somatotroph PitNETs (SGST) stained positive for SF1 (SGST-PIT1). Among DGST, PIT1/SF1 co-expression was significantly associated with scarce FSH/LH expression and fewer fibrous bodies compared to DGST-PIT1. Integrated molecular analyses including publicly available samples confirmed that DGST-PIT1/SF1, DGST-PIT1 and SGST-PIT1 represent distinct tumor subtypes. Clinicopathological meta-analyses indicated that DGST-PIT1 respond more favorably towards treatment with somatostatin analogs compared to DGST-PIT1/SF1, while both these subtypes show an overall less aggressive clinical course than SGST-PIT1. In this study, we spotlight that DGST with co-expression of PIT1 and SF1 represent a common, yet underrecognized, distinct PitNET subtype. Our study questions the rationale of generally classifying such tumors as "plurihormonal", and calls for a refinement of the WHO classification. We propose the term "somatogonadotroph PitNET".