Gastric Cancer — SCE Medical Oncology MCQ

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EasyGI CancersGastric CancerSCE Medical Oncology

A 60-year-old man with advanced gastric cancer is being considered for first-line therapy. HER2 immunohistochemistry testing shows IHC 2+. What additional test is required before treatment selection?

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Correct answer: E — In situ hybridisation for HER2 gene amplification

Explanation lettering: B = shown as A · A = shown as B · E = shown as C · C = shown as D · D = shown as E

In gastric cancer, HER2 positivity is defined by a sequential testing algorithm. When immunohistochemistry (IHC) shows 2+ expression, in situ hybridisation (ISH)—either fluorescence in situ hybridisation (FISH) or chromogenic in situ hybridisation (CISH)—is required to confirm HER2 gene amplification. Only tumours with IHC 2+ AND positive ISH, or IHC 3+ alone, are classified as HER2-positive and eligible for trastuzumab-based therapy. This algorithm is derived from the ToGA trial and is mandated in NICE TA208. PD-L1 testing (A) is relevant for immunotherapy decisions but not for HER2 positivity determination. BRCA testing (B) is not standard in gastric cancer. Repeat IHC (C) is unnecessary if the initial test is adequate. EGFR testing (E) is not required for gastric cancer first-line treatment selection.

Reference: NICE Technology Appraisal TA208: Trastuzumab for the treatment of HER2-positive metastatic gastric cancer. Section 1 Guidance and Background information on HER2 testing algorithm. November 2010. https://www.nice.org.uk/guidance/ta208