Risk of Non-hematologic Cancer in Individuals with High Count Monoclonal B-Cell Lymphocytosis (MBL)

It is unknown whether individuals with monoclonal B-cell lymphocytosis (MBL) are at risk for adverse outcomes associated with chronic lymphocytic leukemia (CLL), such as the risk of non-hematologic cancer. We identified all locally-residing individuals diagnosed with high count MBL at Mayo Clinic between 1999 and 2009 and compared their rates of non-hematologic cancer to that of patients with CLL and two control cohorts: general medicine patients and patients who underwent clinical evaluation with flow cytometry but who had no hematologic malignancy. After excluding individuals with prior cancers, there were 107 high count MBL cases, 132 CLL cases, 589 clinic controls, and 482 flow cytometry controls. With 4.6 years median follow-up, 14 (13%) individuals with high count MBL, 21 (4%) clinic controls (comparison MBL p<0.0001), 18 (4%) flow controls (comparison MBL p=0.0001), and 16 (12%) CLL patients (comparison MBL p=0.82) developed non-hematologic cancer. On multivariable Cox regression analysis, individuals with high count MBL had higher risk of non-hematologic cancer than flow controls (HR=2.36; p=0.04) and borderline higher risk than clinic controls (HR=2.00; p=0.07). Patients with high count MBL appear to be at increased risk for non-hematologic cancer, further reinforcing that high count MBL has a distinct clinical phenotype despite low risk of progression to CLL.