Incidence of chronic lymphocytic leukemia and high-count monoclonal B-cell lymphocytosis using the 2008 guidelines

The 1996 National Cancer Institute Working Group (NCI-WG 96) guidelines classified disease in individuals who had a B-cell clone with chronic lymphocytic leukemia (CLL) immunophenotype as CLL if their absolute lymphocyte count was ≥5 × 10(9)/L. The 2008 International Workshop on CLL guidelines (IWCLL 2008) classified disease as CLL if the absolute B-cell count was ≥5 × 10(9)/L or as monoclonal B-cell lymphocytosis (MBL) if the absolute B-cell count was <5 × 10(9)/L. The objective of the current study of Olmsted County, Minnesota, was to assess the effects of these changes on incidence rates and presentation from 2000 to 2010.

Using diagnostic indices available through the Rochester Epidemiology Project and the Mayo CLL database, the authors identified all patients with newly diagnosed CLL and high-count MBL from 2000 to 2010. Age-specific and sex-specific incidence rates were determined.

According to NCI-WG 96 criteria, there were 115 patients with CLL and 8 patients with MBL during the period studied. Using the IWCLL 2008 classification, there were 79 patients with CLL and 40 patients with MBL. Rai stage distribution (low risk, intermediate risk, and high risk) using NCI-WG 96 criteria was 60.9%, 33.9%, and 5.2%, respectively, compared with 43%, 49.4%, and 7.6%, respectively, using IWCLL 2008 criteria. The age-adjusted and sex-adjusted incidence rates (per 100,000) for CLL and MBL were 10.0 and 0.66, respectively, using NCI-WG 96 criteria versus 6.8 and 3.5, respectively, using IWCLL 2008 criteria. The median time to treatment according to NCI-WG 96 criteria was 9.2 years versus 6.5 years with IWCLL 2008 criteria.

Use of the IWCLL 2008 guidelines reduced the incidence of CLL, altered the distribution of initial Rai stage at diagnosis, and shortened the median time to treatment.