A 58-year-old man from rural India presents with progressive dysphagia, early satiety, and weight loss of 8 kg over 3 months. Upper GI endoscopy reveals a large ulcerated lesion in the gastric antrum with irregular borders and surrounding erythema. Biopsy from the lesion edge shows adenocarcinoma. What is the most appropriate next investigation to determine the extent of local invasion and distant metastases?

Explanation

## Investigation of Choice for Gastric Carcinoma Staging **Key Point:** CT chest and abdomen with IV contrast is the first-line imaging modality for staging gastric carcinoma after histological confirmation, as it assesses both local invasion (T stage) and distant metastases (M stage). ### Role of Each Investigation | Investigation | Primary Role | Timing | Limitation | | --- | --- | --- | --- | | **CT chest + abdomen** | Assess T stage, M stage, distant metastases | After histology confirmed | Limited for T1–T2 lesions; cannot assess N stage accurately | | **EUS ± FNA** | Precise T staging, nodal assessment (N stage) | After histology, before CT | Limited field of view; cannot assess distant metastases | | **PET-CT** | Detect distant metastases, recurrent disease | Selective use in advanced/equivocal cases | High false-positive rate; not routine for primary staging | | **Diagnostic laparoscopy** | Detect peritoneal/liver surface metastases | Preoperative (selected cases) | Invasive; reserved for borderline resectable disease | ### Staging Algorithm for Gastric Cancer ```mermaid flowchart TD A[Histology confirmed: Gastric adenocarcinoma]:::outcome --> B[CT chest + abdomen with IV contrast]:::action B --> C{Resectable disease?}:::decision C -->|Yes, locally advanced| D[EUS for T/N staging]:::action C -->|Yes, early stage| E[Proceed to surgery]:::action C -->|No, metastatic| F[Consider PET-CT for treatment planning]:::action D --> G[Staging laparoscopy if borderline]:::action G --> H[Definitive surgery or neoadjuvant therapy]:::action ``` **High-Yield:** CT is the backbone of staging because it: - Detects distant metastases (liver, peritoneum, lung bases) - Assesses depth of wall invasion (T stage) - Evaluates regional lymph nodes (though less accurate than EUS) - Guides treatment decisions (surgery vs. neoadjuvant therapy) **Clinical Pearl:** EUS is superior for T and N staging in early–intermediate disease but cannot assess distant metastases; it is typically performed *after* CT rules out M1 disease. Diagnostic laparoscopy is reserved for borderline-resectable tumours to detect occult peritoneal disease. **Warning:** ~~PET-CT is NOT routine for primary staging~~ — it is reserved for detecting distant metastases in advanced/equivocal cases or for surveillance post-treatment. [cite:Robbins 10e Ch 17]