A pituitary adenoma resected from a 45-year-old with acromegaly shows Ki-67 of 4% and p53 positivity. Per the WHO 2022 pituitary neuroendocrine tumor (PitNET) classification, this tumor is designated as:

• A GH-producing PitNET, classified by lineage (Pit1 lineage); the Ki-67 and p53 are adjunctive risk stratification markers but do not change the WHO classification designation ✓
• B Pituitary carcinoma, because Ki-67 >3% defines malignancy
• C Aggressive PitNET (formerly 'atypical adenoma'), showing high proliferation index and p53 positivity
• D Intermediate-grade PitNET, WHO grade 2, per the new three-tier grading system

Explanation

WHO 2022 eliminated the 'atypical adenoma' designation and pituitary adenomas are now reclassified as Pituitary NeuroEndocrine Tumors (PitNETs), classified primarily by transcription factor lineage (Pit1 lineage for GH/PRL/TSH tumors; TPIT lineage for ACTH tumors; SF1 lineage for FSH/LH tumors). Pituitary carcinoma is defined exclusively by the presence of cerebrospinal or systemic metastases — NOT by Ki-67, mitotic rate, or p53 status alone. Ki-67 ≥3%, p53 positivity, and high mitotic rate are risk stratification markers for aggressive behavior but do not define a separate WHO classification category. There is no 'intermediate grade' in current WHO 2022 — only PitNET and pituitary carcinoma (metastatic).

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

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Written and medically reviewed by the StethoPrep medical team.