Rochester- September 2024- About 8 to 10 million Americans over age 40 have an overabundance of cloned white blood cells, or lymphocytes, that hamper their immune systems. Although many who have this condition, called monoclonal B-cell lymphocytosis (MBL) — do not experience any symptoms, a new study shows they may have an elevated risk for several health complications, including melanoma, a form of skin cancer. The findings, by Mayo Clinic researchers, are published in a new paper in the Journal of Clinical Oncology.

People with MBL fall along a spectrum that spans from a low amount to a high amount of these dysfunctional lymphocytes. Previous research has shown that MBL is a precursor to a type of blood and bone marrow cancer known as chronic lymphocytic leukemia (CLL). People with CLL also have a heightened risk of melanoma.

“Our study is the first to show that people with this pre-cancerous stage of MBL have a 92% elevated risk of developing melanoma. The risk of melanoma is similar to what we see among people with chronic lymphocytic leukemia,” says Susan Slager, Ph.D., researcher with the Mayo Clinic Comprehensive Cancer Center and senior author of the study.

The findings suggest that having MBL, even at low levels, can serve as a biological signal, or biomarker, for early detection of melanoma, which is increasing worldwide.

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Dr. Slager and her research team have been studying the largest available cohort of individuals — more than 7,000 people screened for MBL through the Mayo Clinic Biobank. The researchers have now followed these individuals for about four years and are finding a collection of potentially related diagnoses among those who screened positive for MBL.

In addition to the increased risk of melanoma, the researchers found that people with MBL were also at higher risk of cancers originating in the lymphatic system and hospitalizations due to serious infections including from COVID-19.

“Previously, scientists would equate MBL as just a part of the aging process. What we’re seeing, though, is there are clinical consequences to having MBL, contracting serious infections and melanoma are some of them,” Dr. Slager says.