Lymphoma is cancer of the lymphoid tissue, which is part of the lymphatic system. A major component of the immune system, the lymphatic system consists of organs, lymph nodes and lymphatic vessels. This system manufactures lymphocytes and transports lymph (fluid made of plasma and white blood cells) from tissues to the bloodstream. Although other forms of cancer may spread to parts of the lymphatic system, lymphoma is the only form that originates in the system.

Lymphoid tissue is formed by various types of immune cells that work together to resist some types of infection and other threats, such as cancer. Lymphocytes are the main type of cell found in the lymphoid tissue. In lymphoma, abnormal lymphocytes continually grow for no reason. This results in abnormal enlargement of the lymph nodes and other body organs containing lymphocytes, causing lumps to develop in the body.

Lymphomas can be categorized into two main groups. One group, characterized by the presence of specific cells (called Reed-Sternberg cells), is known as Hodgkin’s lymphoma or Hodgkin’s disease. All other forms of lymphomas are known as non-Hodgkin’s lymphoma. Cases of non-Hodgkin’s lymphoma are far more common.

Most lymphomas develop as a result of noninherited mutations in the genes of growing lymphocytes. According to the National Cancer Institute (NCI), lymphomas account for about 5 percent of all cases of cancer in the United States. They can occur in both children and adults.