Lymphoma is a cancer that starts in the lymphatic tissue. It is the most common blood cancer and the third most common cancer of childhood.
Cancer of the lymphatic system, which is part of the immune system, can develop when an error occurs in the way a lymphocyte, or white blood cell, is produced, resulting in an abnormal cell. These abnormal cells accumulate two ways: they duplicate faster than normal lymphocytes, or they live longer than normal lymphocytes. The cancerous lymphocytes can grow in many parts of the body, including the lymph nodes, spleen, bone marrow, blood or other organs.
There are two types of lymphomas: Hodgkin's lymphoma, also called Hodgkin's disease, and non-Hodgkin's lymphoma, also called NHL or simply lymphoma.
Hodgkin's lymphoma is marked by the presence of a type of cell called the Reed-Sternberg cell. This type of lymphoma usually starts in the lymph nodes and since lymph tissues all over the body are connected, cancerous lymphocytes can circulate in the lymphatic vessels. As a result, Hodgkin’s lymphoma often spreads from one lymph node to another throughout the body.
Hodgkin’s lymphoma can also spread to other areas and organs outside the lymph system. Unlike other lymphomas, Hodgkin’s lymphoma tends to spread from one lymph node area to the next, skipping areas less frequently than non-Hodgkin's Lymphoma.
Non-Hodgkin's lymphoma is not just one type of disease, but rather a group of at least 30 closely related cancers that affect the lymphatic system. These are the most common lymphomas.
Although the different types of non-Hodgkin's lymphoma have some things in common, particularly their lymphatic origin, they differ in their appearance under the microscope, their molecular features, their growth patterns and their impact on the body.
Non-Hodgkin's lymphoma is broadly divided into two major groups: B-cell lymphomas, which develop from abnormal B-lymphocytes, and T-cell lymphomas, which develop from abnormal T-lymphocytes.