February 11 (HealthDay News) -- Abnormal blood cells can appear in the blood years before a person is diagnosed with chronic lymphocytic leukemia (CCL), U.S. researchers say.

They added that this finding may help improve understanding of cellular changes that occur at the earliest stages of leukemia, and how the disease progresses.

In previous research, the U.S. National Cancer Institute (NCI) team found an abnormal condition called monoclonal B-cell lymphocytosis (MBL) -- in which B-cells in the blood have outer surface proteins similar to proteins found on CLL cells -- in more than 10 percent of family members of CLL patients and in 3 percent to 5 percent of healthy adults over the age of 50. This suggested MBL may be a precursor of CLL.

In this new study, the researchers analyzed frozen samples of blood taken from 45 CLL patients who were cancer-free when they signed up for a national cancer screening trial that included more than 77,000 people. The blood samples revealed that 44 of the 45 CLL patients had MBL between six months to more than six years before their CLL diagnosis.

"Our findings indicate that MBL is present in virtually all of CLL patients prior to full-blown disease," study author author Dr. Ola Landgren, of NCI's Division of Cancer Epidemiology and Genetics, said in an institute news release. "This important discovery provides novel insights into the natural history of CLL and will open new fields of investigation for understanding its causes."

Among people with MBL, the risk of developing CLL is about 1 percent, Landgren said.

The study was published in the Feb. 12 issue of the New England Journal of Medicine.

The next step is to look for differences in MBL cells that may help explain why only some transform into CLL, which usually progresses slowly over many years.

"This finding emphasizes the need to better define predictors of cancer development," NCI Director Dr. John E. Niederhuber said in the news release. "Identifying the earliest indicators of cancer gives researchers an opportunity to study the window from the pre-diagnostic state to the transformation to disease. This may help define risk factors and may allow for the discovery of novel molecular targets for treatment of the disease."

SOURCE: U.S. National Cancer Institute, news release, Feb. 11, 2009