Primary effusion lymphoma (PEL) is a rare type of non-Hodgkin lymphoma that primarily occurs in individuals with weakened immune systems, such as those with HIV/AIDS. It is characterized by the accumulation of malignant lymphocytes in body cavities, leading to fluid buildup, often in the chest or abdomen. PEL is associated with the Kaposi's sarcoma-associated herpesvirus (KSHV), also known as human herpesvirus 8 (HHV-8). Diagnosis typically involves analyzing the fluid from the affected cavities, and treatment may include chemotherapy or targeted therapies to manage the disease and improve the patient's quality of life.