In which stage is lymphoma characterized by involvement of lymph node regions on both sides of the diaphragm?

Lymphoma being characterized by involvement of lymph node regions on both sides of the diaphragm corresponds to Stage III of the staging system used for lymphomas, such as the Ann Arbor classification. In Stage III, the disease is classified as "disseminated," indicating that it has spread to lymph nodes above and below the diaphragm. This stage reflects a more advanced progression of the disease compared to earlier stages, where the involvement is limited to either one side of the diaphragm (Stage I) or two or more lymph node regions on the same side (Stage II). Stage IV indicates extensive disease involvement, including extra-lymphatic sites, which is even more advanced than Stage III. Hence, the correct identification of Stage III highlights the pattern of lymphatic spread characteristic of the disease at this stage.