A 38-year-old woman presents with secondary amenorrhea and galactorrhea. MRI shows a 15 mm pituitary adenoma. Immunohistochemistry of the surgically resected tumor shows strong positivity for prolactin and Pit-1 transcription factor. Per WHO 2022 pituitary adenoma classification, this tumor is reclassified as which entity, and which variant is considered 'high-risk'?

• A Pituitary neuroendocrine tumor (PitNET) of lactotroph lineage (prolactin cell tumor); sparsely granulated lactotroph adenoma in men is high-risk ✓
• B Pituitary adenoma with atypical features; p53 positivity and >3% Ki-67 define high-risk
• C Pituitary carcinoma; defined by CSF or systemic metastasis regardless of Ki-67
• D Craniopharyngioma, adamantinomatous type; positive for Pit-1 and prolactin

Explanation

WHO 2022 reclassifies 'pituitary adenomas' as 'pituitary neuroendocrine tumors (PitNETs),' emphasizing a lineage-based taxonomy using transcription factors (Pit-1, Tpit, SF1, GATA3). A Pit-1-positive prolactin-producing tumor is a lactotroph PitNET. The sparsely granulated lactotroph adenoma (characterized by fibrous bodies and sparse secretory granules, in contrast to densely granulated) in male patients is associated with aggressive behavior, larger size, invasiveness, and resistance to dopamine agonists — making it the high-risk variant. Pituitary carcinoma requires demonstrated metastasis (remote or systemic) by definition.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

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Written and medically reviewed by the StethoPrep medical team.