Chronic lymphocytic leukemia (CLL) is considered to be the most common form for leukemia in adults. With the disease affecting approximately 20,000 Americans every year, CCL can present differently from patient to patient due to a variety of reasons. Clinical tests are conducted to test for biomarkers that can serve as predictors of disease progression or morality. These predictors can then aid doctors in determining an appropriate treatment course specific to that patient. The following article by STAT discusses what exactly goes into testing for these biomarkers as well as how biomarker data can be defined.