A general term to describe an area of altered tissue (e.g., the infected patch or sore in a skin disease).

Small, bean-sized organs of the immune system, distributed widely throughout the body. Lymph fluid is filtered through the lymph nodes in which all types of lymphocytes take up temporary residence. Antigens that enter the body find their way into lymph or blood and are filtered out by the lymph nodes or spleen, respectively, for attack by the immune system.

Cancer of the lymphoid tissues. Lymphomas are often described as being large cell or small cell types, cleaved or non-cleaved, or diffuse or nodular. The different types often have different prognoses (i.e., prospect of survival or recovery). Lymphomas can also be referred to by the organs where they are active, such as CNS lymphomas, which are in the central nervous system, and GI lymphomas, which are in the gastrointestinal tract. The types of lymphomas most commonly associated with HIV infection are called non-Hodgkin's lymphomas or B cell lymphomas. In these types of cancers, certain cells of the lymphatic system grow abnormally. They divide rapidly, growing into tumors.