Facharzt FMH Pathologie Practice Questions - Facharzt FMH Für Pathologie Spécialiste FMH En Pathologie Exam

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A diagnostic biopsy of an advanced gastric adenocarcinoma is submitted for predictive biomarker assessment to determine eligibility for targeted trastuzumab therapy. Immunohistochemistry for HER2 (clone 4B5) is performed. Which of the following staining patterns on a biopsy specimen meets the standard diagnostic criteria for HER2-positive (IHC 3+) status in gastric cancer?

Weak-to-moderate complete membranous staining in >=10% of tumor cells. Strong circumferential membranous staining in >50% of tumor cells only, with incomplete staining interpreted as negative. Nuclear immunoreactivity for HER2 in >20% of viable malignant cells. Strong complete, basolateral, or lateral membranous staining in a cluster of at least 5 contiguous tumor cells, regardless of the overall percentage.

Correct Answer:

Strong complete, basolateral, or lateral membranous staining in a cluster of at least 5 contiguous tumor cells, regardless of the overall percentage.

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