General Pathology USMLE Step 1 Practice Question
A 66-year-old male smoker presents with progressive weight loss, hyponatremia (Na+ 128 mEq/L), and cough. Chest CT reveals a 3-cm central lung mass. Vital signs show BP 138/82, HR 92, RR 18, temp 37°C, SpO2 98% on room air. Biopsy demonstrates sheets of small blue cells with scant cytoplasm, nuclear molding, and high mitotic activity. Electron microscopy shows dense-core neurosecretory granules. Which immunohistochemical stain pattern best confirms this diagnosis?
Answer choices
- ATRAP positive
- BChromogranin and synaptophysin positiveCorrect answer
- CGFAP positive only
- DDesmin positive
- EPSA positive
- FCD56 (NCAM) positivity with negative chromogranin and synaptophysin
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