## Clinical Context This is an early-to-intermediate stage gastric cancer (cT2N0M0 on CT) where accurate locoregional staging is crucial to guide treatment intensity. ### Role of Endoscopic Ultrasound (EUS) **Key Point:** EUS is the most accurate imaging modality for T and N staging in gastric cancer, with sensitivity and specificity >85% for both parameters. It directly influences the decision to give neoadjuvant therapy. **High-Yield:** EUS findings determine treatment strategy: - **T1–T2, N0:** Surgery alone may be sufficient (no clear neoadjuvant benefit in early disease) - **T3–T4 or N+:** Neoadjuvant chemotherapy is indicated ### Why EUS Before Treatment Decision? 1. **Superior accuracy:** CT staging can underestimate T and N stage; EUS is more precise for local invasion and regional nodes. 2. **Guides chemotherapy indication:** If EUS confirms T2N0, surgery alone may be adequate. If EUS reveals T3 or N+ disease, neoadjuvant chemotherapy becomes necessary. 3. **Prevents over- or under-treatment:** Avoids unnecessary chemotherapy in truly early disease or ensures chemotherapy is given in locally advanced disease. 4. **Standard practice:** EUS is recommended in the workup of gastric cancer before treatment decisions in most guidelines (NCCN, ESMO, IGCA). ### Decision Tree After EUS ```mermaid flowchart TD A[EUS for T and N staging]:::action --> B{T and N stage?}:::decision B -->|T1-T2, N0| C[Surgery alone: Subtotal/total gastrectomy + D2 LND]:::action B -->|T3-T4 or N+| D[Neoadjuvant chemotherapy]:::action D --> E[Reassess with CT/EUS]:::action E --> F[Surgery if resectable]:::action C --> G[Adjuvant chemotherapy if high-risk features]:::action ``` **Clinical Pearl:** In a patient with cT2N0 disease on CT, EUS may upstage to T3 or reveal occult nodal disease, fundamentally changing the treatment approach. This is why EUS is performed before committing to a treatment plan. ### Why Not the Other Options? | Option | Why Not | |--------|----------| | Direct total gastrectomy | Skips EUS staging; may miss T3 or N+ disease that would benefit from neoadjuvant therapy; risks inadequate treatment | | Immediate neoadjuvant chemotherapy | Premature without accurate staging; if EUS confirms T2N0, chemotherapy may be unnecessary and exposes patient to toxicity without proven benefit | | Diagnostic laparoscopy | Not indicated in cM0 disease on CT; adds morbidity without changing management in a patient without imaging evidence of peritoneal disease | [cite:NCCN Gastric Cancer Guidelines, ESMO Gastric Cancer Guidelines 2023]
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