## Histological Classification of Epithelial Ovarian Cancer **Key Point:** Serous cystadenocarcinoma accounts for approximately 40–50% of all epithelial ovarian cancers, making it the single most common histological subtype. ### Frequency Distribution | Histological Type | Frequency | Grade | Prognosis | | --- | --- | --- | --- | | Serous | 40–50% | Often high-grade | Intermediate | | Mucinous | 10–15% | Often low-grade | Better (early stage) | | Clear cell | 5–10% | Often high-grade | Worse | | Endometrioid | 10% | Often low-grade | Better | | Brenner | 2–5% | Low-grade | Excellent | **High-Yield:** Serous tumors are further subdivided into low-grade (LGSC) and high-grade (HGSC) variants. High-grade serous carcinoma (HGSC) is the most aggressive form and accounts for ~70% of ovarian cancer deaths. **Clinical Pearl:** Mucinous ovarian cancers, while less common, are often diagnosed at earlier stages and have better outcomes when confined to the ovary. However, they are associated with appendiceal primary tumors in 5–10% of cases, necessitating careful assessment of the appendix during surgery. **Mnemonic:** **SMCEB** — Serous, Mucinous, Clear cell, Endometrioid, Brenner (in order of decreasing frequency among epithelial subtypes). ### Why Serous is Most Common Serous tumors arise from the coelomic epithelium lining the ovarian surface and represent the natural evolution of serous cystadenomas to carcinomas. The malignant potential of serous lesions is higher than mucinous variants, contributing to their predominance in clinical practice. [cite:Robbins 10e Ch 22]
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