Narrator: This is Science Today. Over the last two decades, the incidence rate of non-Hodgkin's lymphoma - has nearly doubled. Today, it's the country's fifth most common cancer in both men and women. According to Elizabeth Holly, a professor of cancer epidemiology studies at the University of California, San Francisco - the disease is steadily rising.
Holly: The increase in incidence is about four percent per year in men and about three percent per year in women and we don't really understand why this disease is increasing at this rate.
Narrator: Many researchers believe there's a genetic factor in lymphoma which is "triggered," by an environmental factor, so Holly is conducting a large study on potential risk factors, including occupation, medical history and lifestyle.
Holly: We really need to have a better understanding about risk factors for this disease with the goal towards getting the word out so that people can change their behaviors or whatever it is that's happening that may influence getting non-Hodgkin's lymphoma.
Narrator: For Science Today, I'm Larissa Branin.