A variety of systems have been used to classify NHL sub-types according to their microscopic appearance and the behavior of the disease. The Rappaport classification is an older scheme still commonly used. More recently, an international group of pathologists and clinicians developed a Working Formulation to establish a common terminology. This defined 10 major sub-types categorized as low-, intermediate- or
high-grade. These terms relate to the relative malignant potential characterized by a growth rate
that may be low (slow), high (rapid) or intermediate (moderately rapid).
How It Spreads Since lymphocytes normally travel throughout the body via the blood and the lymphatic system , malignant lymphomas can either start in or spread to virtually any organ.
A lymphoma may arise in a single lymph node or organ and stay there even when a large mass is present, or many different sites may be involved at the time of diagnosis. Low-grade lymphomas most often involve lymph nodes , bone marrow and the spleen when they are diagnosed. Intermediate- and high-grade lymphomas are most commonly found in lymph nodes, but about one-third of cases primarily involve organs separate from lymph nodes and are called extranodal.
What Causes It The immune system is so complex and dynamic that there are many opportunities for errors in regulation. Many lymphomas are thought to result from such errors or "accidents," which are statistically more probable when the immune system is continually stimulated.
