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NBME 16 Answers

nbme16/Block 3/Question#32 (5.3 difficulty score)
A 65-year-old woman comes to the physician ...
Pulmonary small cell carcinoma metastatic to the brain🔍

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The patient has a brain cancer, which is 50/50 between primary cancer and metastasis (lung most common; also breast, colon).

The answer is small cell carcinoma of the lung versus a primary brain cancer because there are cells staining positive for carcinoma marker (cytokeratin) and neuroendocrine markers (chromogranin and synaptophysin), which is what SCLC is.

cassdawg  Another reason this is small cell lung cancer is the weakness of the proximal upper and lower extremities while also having augmentation (increasing) of strength with repetitive stimulation. This is characteristic of Lambert-Eaton myasthenic syndrome [where strength increases with stimulation; opposite of myasthenia gravis]. Lambert-Eaton can be caused by a paraneoplastic syndrome of small cell lung cancer (FA2020 p228 and 472) +3  
passplease  What about the fact that it is a single well-demarcated mass. Wouldnt metastatic cancer present as multiple masses? This made me think primary brain cancer. +2  
jaeyphf  @passplease I originally thought this way too and it fucked me. I think the easiest way is elimination + staining. Pt is an adult - eliminate neuroblastoma, ependymoma as both are more common in kids Pt is not immunocompromised - eliminate CNS lymphoma GBM does not stain positive for cytokeratin, chromogranin, synaptophysin - eliminate GBM Left with Small cell carcinoma +