• The diagnosis of non-Hodgkin lymphoma encompasses a wide spectrum of lymphoid-derived tumors
• More than 10 distinct tumor subtypes with variable biologic behavior
• Non-Hodgkin lymphoma may originate from B cells, T cells, or histiocytes
• In contrast to Hodgkin lymphoma, lymph node tumor involvement is more likely to spread in a noncontinous fashion in non-Hodgkin lymphoma
• Prognosis and treatment is more dependent on the grade and type of malignancy in contrast to the importance of clinical stage in Hodgkin lymphoma
• Functionally separated into low-grade and high-grade groups
• 33% of cases arise outside of the lymph nodes: oropharynx, paranasal sinuses, thyroid, GI tract, liver, testicles, skin, bone marrow, and CNS
• Most common extranodal site is the stomach, accounting for 50% of all GI lymphomas
• Most accepted classification system is the Revised European-American Lymphoma (REAL) classification