A 48-year-old woman with biopsy-proven nasopharyngeal carcinoma (undifferentiated squamous cell type) is being staged for treatment planning. She is asymptomatic for distant metastases. Which investigation is most appropriate as the next step to detect occult metastatic disease and guide treatment intensity?

Explanation

## Staging Investigation for Nasopharyngeal Carcinoma **Key Point:** 18F-FDG PET-CT is the most sensitive and specific investigation for detecting occult metastatic disease in nasopharyngeal carcinoma and is essential for treatment planning and prognostication. ### Why PET-CT for Staging? 1. **Highest sensitivity for metastases** — Detects bone, lung, liver, and nodal metastases with >90% sensitivity 2. **Metabolic imaging** — FDG uptake reflects tumor aggressiveness and glucose metabolism 3. **Whole-body assessment** — Single imaging modality evaluates primary tumor, regional nodes, and distant metastases simultaneously 4. **Prognostic value** — Guides treatment intensity (concurrent chemoradiation vs. chemotherapy alone) 5. **Standard of care** — Recommended by NCCN and ESMO guidelines for all newly diagnosed nasopharyngeal carcinoma ### Staging Algorithm for Nasopharyngeal Carcinoma ```mermaid flowchart TD A[Biopsy-proven NPC]:::outcome --> B[Local/regional staging]:::action B --> C[CT/MRI head and neck]:::action C --> D[Assess for metastases]:::decision D --> E[18F-FDG PET-CT whole body]:::action E --> F{Metastases detected?}:::decision F -->|Yes| G[Stage IV - Systemic therapy]:::outcome F -->|No| H[Stage I-III - Locoregional therapy]:::outcome H --> I[Concurrent chemoradiation ± induction chemotherapy]:::action ``` ### Comparison of Staging Investigations | Investigation | Sensitivity for Metastases | Primary Tumor Assessment | Cost | Radiation Dose | |---|---|---|---|---| | Chest X-ray + Abdominal US | 60–70% | Poor | Low | Minimal | | 18F-FDG PET-CT | 90–95% | Excellent | High | Moderate | | Bone scan (Tc-99m) | 70–80% (bone only) | None | Moderate | Moderate | | Brain MRI | 95% (brain only) | None | High | None | **High-Yield:** PET-CT changes management in ~30% of nasopharyngeal carcinoma cases by detecting occult metastases that would otherwise be missed on conventional imaging. **Clinical Pearl:** In nasopharyngeal carcinoma, the most common sites of metastatic spread are **bone (40%), lung (30%), and liver (20%)**. PET-CT detects all three with superior sensitivity compared to conventional imaging. **Mnemonic: PET-CT for NPC Staging** — **P**rimary tumor extent, **E**xtent of regional nodes, **T**reatment planning, **C**omplete body survey, **T**umor burden assessment.