The following is provided by the National Cancer Institute

Lymphoma is a general term for cancers of the lymphatic system—an important part of the body’s immune system that fights disease and infection. About five percent of all cancers in the United States are lymphomas.

There are two types of lymphoma: Hodgkin’s disease is one of these two types. All other types of lymphomas are considered non-Hodgkin’s lymphoma (NHL).

According to the National Cancer Institute, since 1973 the incidence of non-Hodgkin’s lymphoma in the United States has increased about 75 percent – one one of the largest increases among major cancer sites. NCI has estimated that about 1 in 52 men and 1 in 61 women in the United States will be diagnosed with NHL during their lifetime.

Part of the increase in NHL incidence in recent years is a result of the AIDS epidemic: NHL is 60 times more common among AIDS patients than in the general U.S. population.

Herbicides and insecticides have been linked to risk for NHL in studies of farmers, pesticide applicators, and other occupational groups exposed to high levels of these chemicals. An NCI study found that contamination of drinking water with nitrate, a chemical found in fertilizers, may also be associated with an increased risk of NHL, particularly in agricultural areas.

In a normal immune system, the job of B-Cells is to fight bacteria. B-Cell lymphoma occurs when a B-Cell mutates and becomes cancerous. After this occurs, every time this cancerous B-Cell clones itself, the new cell maintains the structure of the mutated cell. Because of this, every person's B-Cell lymphoma cells are unique.