We were intrigued by recent hospital-based case series suggesting that patients with MBL are at increased risk for CLL23,26 and wanted to test the hypothesis that CLL is typically preceded by MBL as a precursor state. Among 77,469 healthy adults who were enrolled in the nationwide, population-based PLCO Cancer Screening Trial,27 we identified 45 patients who were subsequently diagnosed with CLL and had prospectively stored prediagnostic peripheral-blood samples, which had been obtained up to 6.4 years earlier. Using six-color flow cytometry and IGHV gene-rearrangement analysis by RT-PCR, we found evidence of prediagnostic monoclonality among B cells (by either of the two methods) in 44 patients (98%; 95% CI, 88 to 100). In 41 patients (91%; 95% CI, 79 to 98), the clone was confirmed by both methods.
