MON-103 - A Case of Plurihormonal Pituitary Neuroendocrine Tumor Presenting as Acromegaly

Plurihormonal pituitary adenomas are rare pituitary neuroendocrine tumors (PitNETs) defined by secretion of two or more hormones and characterized by immunohistochemical profiling [1]. The 2022 World Health Organization classification recognizes three subtypes: immature PIT1-lineage tumors, mature plurihormonal PIT1-lineage tumors, and rare plurihormonal tumors with multi-lineage differentiation [2].
A 34-year-old male underwent routine brain MRI for surveillance of partial corpus callosum agenesis and was incidentally found to have a 3.2 cm pituitary macroadenoma compressing the optic chiasm. Preoperative biochemical evaluation demonstrated markedly elevated insulin-like growth factor-1 (IGF-1) of 1172ng/mL (132 – 333ng/mL) and growth hormone (GH) of 61.9ng/mL ( < 7.1ng/mL). Morning cortisol levels were mildly elevated two times at 23.5 and 27.2mcg/dL (4 – 22mcg/dL) with an adrenocorticotropic hormone (ACTH) level of 24pg/mL (6 – 50pg/mL). Hypogonadotropic hypogonadism was present with Luteinizing Hormone (LH) of 1.1mIU/mL (1.5 – 9.3mIU/mL), Follicular Stimulating Hormone (FSH) of 2.1 (1.4 – 12.8mIU/mL) and Total Testosterone of 291.2ng/dL (264 – 916ng/dL). Physical examination revealed classic features of acromegaly: frontal bossing, broad prominent nose, and bilateral enlargement of the hands and feet. His mother reported gradual changes in appearance over seven years, initially attributed to baseline intellectual disability. Patient underwent transsphenoidal resection. Post operative MRI showed no evidence of gross residual tumor. Pathology demonstrated a plurihormonal pituitary adenoma with positive immunohistochemical staining for PIT1, steroidogenic factor-1 (SF1), somatostatin receptor 2A (SSTR2A), and GATA binding protein-3 (GATA3). Twelve weeks postoperatively, IGF-1 had decreased to 307ng/mL, with normalization of remaining pituitary hormones (GH 0.5ng/mL, ACTH 30.2pg/mL, morning cortisol 16.5mcg/dL, LH 2.6mIU/mL, FSH 1.7mIU/mL). Salivary cortisol testing was negative for Cushing syndrome.
PitNETs co-expressing PIT1 and SF1 represent a rare multilineage subtype that typically present as large macroadenomas with biochemical and clinical features of acromegaly consistent with the presentation observed in this patient [3]. This case underscores the diagnostic value of immunohistochemistry in accurate classification of plurihormonal PitNETs.
1. Dumitriu-Stan, RI., et al., Plurihormonal Pituitary Neuroendocrine Tumors: Clinical Relevance of Immunohistochemical Analysis. Diagnostic (Basel), 2024. 14(2)
2. Asa, SL., O. Mete, A. Perry, and RY. Osamura, Overview of the 2022 WHO Classification of Pituitary Tumors. Endocrine Pathology, 2022. 33(1): p 6-26
3. Asa, SL., O. Mete, N.D. Riddle, and A. Perry, Multilineage Pituitary Neuroendocrine Tumors (PitNETs) Expressing PIT1 and SF1. Endocrine Pathology, 2023. 34(3): p 273-278

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