**Core Concept**
Primary central nervous system lymphoma (PCNSL) is a type of non-Hodgkin lymphoma that primarily affects the brain and eyes of immunocompromised individuals, such as those with AIDS. This condition arises due to the abnormal proliferation of lymphocytes in the central nervous system, which is often unresponsive to systemic chemotherapy.

**Why the Correct Answer is Right**
The acquired immunodeficiency syndrome (AIDS) significantly impairs the body's immune response, making individuals more susceptible to opportunistic infections, including those caused by the Epstein-Barr virus (EBV). EBV is known to be associated with the development of primary central nervous system lymphoma (PCNSL) in immunocompromised patients. The pathogenesis of PCNSL involves the clonal expansion of EBV-infected B cells, which infiltrate the brain and lead to aggressive tumor growth.

**Why Each Wrong Option is Incorrect**
* **Option A:** Glioblastoma multiforme is the most common primary brain tumor in adults but is not specifically associated with AIDS.
* **Option B:** Metastatic brain tumors are more common than primary brain tumors and are often seen in patients with a history of cancer. However, they are not typically linked to AIDS.
* **Option C:** Cerebral toxoplasmosis is a common opportunistic infection in AIDS patients, but it is caused by the parasite Toxoplasma gondii, not a tumor.

**Clinical Pearl / High-Yield Fact**
PCNSL often presents with nonspecific symptoms such as headache, confusion, and seizures, making it challenging to diagnose. Imaging studies, such as MRI, are essential for detecting PCNSL, which typically appears as multiple, ring-enhancing lesions in the brain.

**Correct Answer: C. Primary central nervous system lymphoma (PCNSL).**