## Histological Classification of Nasopharyngeal Carcinoma **Key Point:** Non-keratinizing squamous cell carcinoma (undifferentiated type), also known as WHO Type III or Regaud carcinoma, is the predominant histological subtype globally, accounting for ~95% of cases. ### WHO Classification of Nasopharyngeal Carcinoma | Histological Type | Frequency | EBV Association | Geographic Pattern | | --- | --- | --- | --- | | **Non-keratinizing (undifferentiated)** | ~95% | Strong (>95%) | Worldwide, especially endemic areas | | Keratinizing | ~3–5% | Weak–moderate | North Africa, Middle East | | Adenocarcinoma | <1% | Weak | Sporadic | | Basaloid squamous cell | Rare | Variable | Sporadic | **High-Yield:** The undifferentiated subtype shows: - Syncytial growth pattern with indistinct cell borders - Prominent lymphoid infiltrate (lymphoepithelioma) - Nearly universal EBV positivity (detected by in situ hybridization for EBER) - Best prognosis among squamous subtypes when treated with concurrent chemoradiation **Clinical Pearl:** EBV serology (anti-VCA-IgA, anti-EBNA) is used for screening in endemic regions and post-treatment surveillance. Rising titers may indicate recurrence. **Mnemonic: "UNK" = UNdifferentiated, 95% worldwide, Known for EBV** 
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