## Pathological Features and Staging of Nasopharyngeal Carcinoma ### Histological Classification **Key Point:** The WHO classifies NPC into four histological subtypes: 1. **Keratinizing** — more common in non-endemic areas (North Africa, Middle East) 2. **Differentiated non-keratinizing** 3. **Undifferentiated non-keratinizing** — most common in endemic areas (Southeast Asia, Southern China) 4. **Basaloid squamous cell carcinoma** **High-Yield:** In endemic regions like Southeast Asia, **undifferentiated squamous cell carcinoma** (not keratinizing) is the predominant type. This is strongly associated with EBV and carries better prognosis than keratinizing variants. ### Geographic Variation in Histology | Region | Predominant Type | EBV Association | | --- | --- | --- | | Endemic (SE Asia, South China) | Undifferentiated non-keratinizing | >95% | | Non-endemic (North Africa, Middle East) | Keratinizing | 25–50% | | Non-endemic (Western countries) | Keratinizing | <10% | **Clinical Pearl:** The undifferentiated type in endemic areas is sometimes called "WHO Type III" and has the strongest EBV association and relatively better chemotherapy response. ### Clinical Presentation and Lymph Node Involvement **High-Yield:** Early cervical lymph node metastases are a hallmark of NPC: - Present in >80% of cases at diagnosis - Often the presenting symptom (cervical mass, serous otitis media from Eustachian tube obstruction) - Bilateral involvement is common (30–50% of cases) - Distant metastases (bone, lung, liver) occur in 20–30% at presentation ### TNM Staging **Key Point:** NPC uses a **separate TNM classification** (AJCC 8th edition, 2017) distinct from other head and neck cancers because: - Anatomy and lymphatic drainage are unique - Early lymph node involvement is characteristic - Staging criteria differ (e.g., T1 includes tumors confined to nasopharynx; N staging includes retropharyngeal nodes) **Warning:** Do not use the standard oropharyngeal/laryngeal TNM for NPC — the criteria are different. ### Why the Distractor Is Wrong Keratinizing SCC is the predominant type in **non-endemic** areas (North Africa, Middle East), NOT in endemic Southeast Asian populations. In endemic regions, **undifferentiated non-keratinizing** carcinoma is most common. [cite:AJCC Cancer Staging Manual 8e; Harrison 21e Ch 105]
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