What is Clonal Cytopenia of Undetermined Significance (CCUS)?

CCUS is a condition in which a person has a low blood count—a low level of certain kinds of blood cells—without an apparent cause, and a portion of the blood cells carry an acquired genetic mutation. The condition, which is usually diagnosed after a routine blood test followed by specialized molecular testing, can place individuals at increased for certain blood-related cancers.

People with CCUS have a 75% chance of developing myelodysplastic syndrome (MDS)—a disorder in which certain blood cells fail to develop and function properly—or a related condition within four to five years. By contrast, people with unexplained low blood counts whose blood cells don’t have a genetic mutation have a much lower risk (around 10%) of developing MDS or related condition after five years.

When an individual is found to have a low blood count, doctors conduct a thorough exam to determine whether it’s caused by a vitamin deficiency, use of certain medications, heavy alcohol consumption, blood cancer, or other known triggers. When such causes are identified, the problem can often be remedied with medical treatment or lifestyle changes. When no such explanation can be found, DNA testing of the blood for certain mutations can be considered. If some of the blood cells test positive for certain mutations, CCUS is diagnosed.

Severely low blood counts can produce significant health problems, regardless of whether the blood cells harbor genetic mutations, according to David Steensma, MD, clinic director of the Center for the Prevention of Progression (CPOP) at Dana-Farber. People with sharply low red blood cell counts may experience fatigue or shortness of breath. Those with very low white blood cell counts may have an increased risk of infection, and those with low platelet counts may be at increased risk of bruising and bleeding.

Adam Sperling, MD, PhD, and Lachelle Weeks, MD, PhD, of the Center for Prevention of Progression at Dana-Farber.
Adam Sperling, MD, PhD, and Lachelle Weeks, MD, PhD, of the Center for Prevention of Progression at Dana-Farber.

People identified as having CCUS are monitored closely with periodic blood tests to catch the onset of MDS—if it occurs—as early as possible, when treatment can be most effective. Steensma and his colleagues in the CPOP are working to better understand the biological mechanisms that make CCUS a risk factor for MDS, with the goal of devising ways of preventing the progression of the disease.