What characterizes Stage I in Ann Arbor staging?

Stage I in the Ann Arbor staging system is characterized by the involvement being localized to a single lymph node or a single extralymphatic site. This indicates that the disease has not spread extensively beyond this initial site, which is crucial for treatment and prognosis.

Understanding the importance of localization in Stage I is essential when considering the management of lymphomas, as early-stage disease often has a significantly better prognosis compared to more advanced stages. In contrast to the other stages, which involve broader dissemination or multiple affected sites, Stage I represents the most localized form of disease, making it a key point for both diagnosis and treatment planning.