Definition of Non-Hodgkin's lymphoma:

Non-Hodgkin's lymphoma is cancer of the lymphoid tissue, which includes the lymph nodes, spleen, and other organs of the immune system.

Causes, incidence, and risk factors:

White blood cells called lymphocytes are found in lymph tissues. They help prevent infections. Most lymphomas start in a type of white blood cells called B lymphocytes, or B cells.

For most patients, the cause of this cancer is unknown. However, lymphomas may develop in people with weakened immune systems. For example, the risk of lymphoma increases after an organ transplant or in people with HIV infection.

There are many different types of non-Hodgkin's lymphoma. It is classified according to how fast the cancer spreads.

• The cancer may be low grade (slow growing), intermediate grade, or high grade (fast growing). Burkitt's tumor is an example of a high-grade lymphoma. Follicular lymphoma is a low-grade lymphoma
• The cancer is further sub-classified by how the cells look under the microscope, for example, if there are certain proteins or genetic markers present.

According to the American Cancer Society, a person has a 1 in 50 chance of developing non-Hodgkin's lymphoma. Most of the time, this cancer affects adults. However, children can get some forms of lymphoma. High-risk groups include those who have received an organ transplant or who have a weakened immune system.

This type of cancer is slightly more common in men than in women.