A 65-year-old man is diagnosed with a well-differentiated pancreatic neuroendocrine tumor (PanNET). Pathology shows Ki-67 of 8% and 7 mitoses per 10 HPF. According to the 2022 WHO classification, this tumor is best classified as:
- A PanNET G1 (Ki-67 <3%, <2 mitoses/10 HPF)
- B PanNET G3 (Ki-67 >20%, >20 mitoses/10 HPF)
- C PanNET G2 (Ki-67 3–20%, 2–20 mitoses/10 HPF) ✓
- D Pancreatic neuroendocrine carcinoma (NEC), large cell type
Correct answer: C. PanNET G2 (Ki-67 3–20%, 2–20 mitoses/10 HPF)
Explanation
The 2022 WHO classification grades well-differentiated PanNETs as G1 (Ki-67 <3% AND <2 mitoses/10 HPF), G2 (Ki-67 3–20% OR 2–20 mitoses/10 HPF), or G3 (Ki-67 >20% OR >20 mitoses/10 HPF). The discordance rule dictates grading by the higher category — here Ki-67 8% falls in G2 and mitotic count 7/10 HPF also in G2, hence G2. Poorly differentiated carcinomas (NEC) are biologically distinct, with small-cell or large-cell morphology and Ki-67 typically >55%.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
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Written and medically reviewed by the StethoPrep medical team.