I tried to reason out what had happened, but could not fit any of the known factors together, and finally gave the matter up.

In fact, 75% of all women with breast cancer have no known risk factors.

There are no known risk factors that have been identified specific to the disease.

Age is the most important known risk factor for Alzheimer's disease.

You are younger than 35 and have no known risk factors for Down syndrome or other problems.

And most people who get leukemia do not have any known risk factors.

In fact, most children with leukemia don't have any known risk factors.

As well, James was a known factor and he didn't relish giving that up.

"The weight gain itself is a known risk factor for diabetes."

However, there are a few known risk factors for this type of leukemia.