A tumor specimen stains positive for chromogranin A, synaptophysin, and Ki-67 index is measured at 22%. According to the WHO 2022 classification of neuroendocrine neoplasms, this tumor is best classified as:

• A Well-differentiated neuroendocrine tumor (NET) G3 ✓
• B Well-differentiated neuroendocrine tumor (NET) G2
• C Poorly differentiated neuroendocrine carcinoma (NEC), large cell type
• D Mixed neuroendocrine-non-neuroendocrine neoplasm (MiNEN)

Explanation

WHO 2022 classifies neuroendocrine neoplasms into well-differentiated NETs (G1: Ki-67 <3%, G2: Ki-67 3–20%, G3: Ki-67 >20%) and poorly differentiated NECs. A Ki-67 of 22% with preserved chromogranin and synaptophysin positivity (indicating morphological well-differentiation) places this tumor in the NET G3 category — a critical distinction because NET G3 has better prognosis and different therapeutic approach compared to poorly differentiated NEC. NEC (large cell or small cell type) is morphologically poorly differentiated with high mitotic rate and typically Ki-67 >50–80%; MiNEN requires a non-neuroendocrine component comprising >30% of the tumor.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.