Knoxville (WVLT) - Thompson says he was diagnosed with Non-Hodgkin's Lymphoma more than two years ago.

He says the disease is in remission, with no illness or symptoms.

Medical Reporter Jessa Goddard takes a look at the disease itself, and how it affects life expectancy.

Non-Hodgkin's Lymphoma is cancer of the cells of the lymphatic system.

It can start almost anywhere in the body.

And it can spread to almost any part of the body.

"I wouldn't be doing this if I wasn't satisfied in my own mind as to the nature of it and the fact that not only will I have an average lifespan but in the meantime I will not be affected in anyway by it," says UT Medical Center oncologist Dr. Wahid Hanna.

There are many different types of Non-Hodgkin's Lymphoma. In the low-grade lymphoma, which Fred Thompson has revealed he has, the lymphomas grow slowly and cause few symptoms early in the disease.

"Sometimes the patients will not have any symptoms and sometimes they will have fever, and chills and night sweats and weight loss," Dr. Hanna says.

But the most common symptom is a painless swelling of the lymph nodes.

"When you have a cold, you have lymph nodes, or lumps in here, these are the lymph nodes and when you have malignant lymphoma, these lymph nodes are attacked by the malignant cells," Dr. Hanna says.

The type of Non-Hodgkin's Lymphoma is diagnosed by how the cancer cells look under a microscope and how quickly they are likely to grow.

It's different from Hodgkin's Lymphoma and occurs eight times more often.

It's more common in men than women, and the likelihood of getting it increases as you get older.

Treatment depends on the stage and grade of the disease, the patient's age and general health, but varies from watchful waiting to chemotherapy.

"It's one of the diseases that we can say with the proper treatment, we can talk about remission in 70 to 90 percent, or so," Dr. Hanna explains.

Thompson says he's been in remission for nearly three years, a patient is considered cured there is no relapse after five.

There are more than 30 different subtypes of the disease.

And survival varies widely, depending on the subtype, but overall the five year survival is 63 percent.