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.