طب الأورام

Case 1:
A 45-year-old right-handed man who has been HIV positive for the past 3 years has noticed some sort of visual change over the past 1 to 2 months. It is difficult for him to describe, but it is some sort of distortion of part of his right visual field. There is a 4-cm rim-enhancing lesion in the left occipital lobe that is revealed by MRI. Which of the following tumor types is common in the brain of patients with AIDS, but otherwise extremely rare?
Lymphocytic leukemia
Metastatic lymphoma
Primary lymphoma
Kaposi's sarcoma
Lymphosarcoma

A 15-year-old with tibial pain (which is worse at night and relieved by aspirin) has a small hypodense area surrounded by reactive bone formation on x-ray. What is the likely diagnosis?