Lymphoma is a kind of cancer that starts in the lymphatic system. The lymphatic system is part of the immune system, and helps rid the body of toxins, waste and other unwanted materials. 

There are two main types of lymphomas. One is Hodgkin lymphoma, sometimes called Hodgkin disease, while the other types of lymphoma are grouped together and called non-Hodgkin lymphomas.

With both Hodgkin lymphoma and non-Hodgkin lymphoma, cells in the lymphatic system grow out of control, creating a mass of extra cells that can form a tumor. Since the types of lymphoma grow at different rates, they are treated in different ways.