What is Lymphoma? Lymphoma is a cancer that begins in the lymphatic system—the body's primary disease-fighting network. This intricate system includes your lymph nodes (glands), spleen, thymus gland, and bone marrow. [Image of the human lymphatic system] The Mechanism: It occurs when lymphocytes (a vital type of white blood cell) undergo a DNA mutation and begin to grow uncontrollably. Because lymphatic tissue is found throughout the entire body, lymphoma can originate almost anywhere. Hodgkin's vs. Non-Hodgkin's: What's the Difference? If you or a loved one is diagnosed, the first task for oncologists is to determine which of the two main categories the lymphoma falls into. This critical distinction is made by examining the cancer cells under a high-powered microscope. Feature Hodgkin's Lymphoma (HL) Non-Hodgkin's Lymphoma (NHL) ...