HIV-Positive Male Presents With Multiple Symptoms and Has a History of Colonic Polyps

A 20-year-old HIV positive male presents with headache, nausea, and vomiting following a seizure. History is notable for three surgeries to remove colonic polyps. Subsequent MRI brain scan with contrast reveals a mass in the left frontal lobe which is removed. The image above is an H&E stained section of the mass.

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The most likely diagnosis is: