A 55-year-old postmenopausal woman presents with postmenopausal bleeding. Endometrial biopsy shows complex hyperplasia with marked nuclear atypia, crowded glands, and mitotic activity. According to the WHO 2020 classification, this lesion is now classified as:

• A Simple endometrial hyperplasia without atypia
• B Endometrial intraepithelial neoplasia (EIN) — precursor of endometrioid carcinoma ✓
• C Serous endometrial intraepithelial carcinoma (SEIC)
• D Low-grade endometrioid adenocarcinoma

Explanation

The WHO 2020 classification of endometrial hyperplasia recognizes two categories: (1) Hyperplasia without atypia (benign, low malignant potential, responds to progestins) and (2) Atypical hyperplasia/Endometrial Intraepithelial Neoplasia (EIN) — a clonal premalignant lesion characterized by glandular crowding (>50% gland:stroma ratio), nuclear atypia, and cytological changes distinct from background endometrium. EIN has ~30% risk of concurrent endometrial carcinoma and ~25% progress to endometrioid adenocarcinoma if untreated. The old complex/simple hyperplasia terminology has been replaced by this two-tier system in WHO 2020.

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

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Written and medically reviewed by the StethoPrep medical team.