## Histological Types of Endometrial Cancer **Key Point:** Endometrioid adenocarcinoma accounts for approximately 70–80% of all endometrial cancers and is the most common histological type. ### Frequency Distribution | Histological Type | Frequency | Grade | Prognosis | | --- | --- | --- | --- | | Endometrioid adenocarcinoma | 70–80% | Grade 1–3 | Favorable (early stage) | | Serous adenocarcinoma | 10% | High grade | Poor (aggressive) | | Clear cell carcinoma | 4–5% | High grade | Poor (aggressive) | | Squamous cell carcinoma | <1% | Variable | Rare | | Mucinous adenocarcinoma | 1–2% | Low grade | Favorable | ### Clinical Features of Endometrioid Type 1. **Association with estrogen excess:** Most commonly arises in the setting of unopposed estrogen (obesity, PCOS, estrogen-secreting tumors). 2. **Early presentation:** Often presents at early stage (Stage I–II) due to postmenopausal bleeding as an early symptom. 3. **Better prognosis:** 5-year survival ~85% when diagnosed at early stage. 4. **Molecular profile:** Type I cancer (microsatellite instability, PTEN mutations, KRAS mutations). ### Why Other Types Are Less Common **Serous adenocarcinoma** (10%): High-grade, aggressive, often presents at advanced stage despite lower frequency. Associated with p53 mutations (Type II cancer). **Clear cell carcinoma** (4–5%): Rare, high-grade, poor prognosis. Often seen in older women. **Squamous cell carcinoma** (<1%): Extremely rare; usually arises from chronic irritation or metaplasia. **High-Yield:** The vast majority of endometrial cancers are adenocarcinomas, and endometrioid is by far the most common subtype. This is the "bread and butter" of endometrial cancer pathology. **Clinical Pearl:** Endometrioid adenocarcinoma with early postmenopausal bleeding has an excellent prognosis with surgery alone (total abdominal hysterectomy + bilateral salpingo-oophorectomy) in early-stage disease. [cite:Robbins 10e Ch 22]
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