CLL/SLL Is More Common Than Registry Incidence Suggests: A Population-Based Study in Manitoba, Canada.

Background: The exact incidence of chronic lymphocytic leukemia (CLL) and small lymphocytic lymphoma (SLL) is unknown. In the appropriate clinical setting, peripheral blood immunophenotyping is often sufficient for diagnosis. Cancer registries that rely only on histological or cytological reporting may inaccurately estimate the incidence of CLL/SLL. The province of Manitoba, with a population of 1.2 million people, has a centralized flow cytometry service as well as a provincial cancer registry. We thus had the opportunity to use these large databases to describe the demographic and clinical patterns of CLL/SLL. This has enabled us to test the hypothesis that registry data underestimates the incidence of this disease.

Methods: All patients diagnosed with CLL/SLL between January 1, 1998 and December 31, 2003 were obtained from the Manitoba cancer registry and the central flow cytometry database. Additional clinical characteristics were obtained from a chart review.

Results: 491 patients were diagnosed by flow cytometry. In contrast, cancer registry data reported 345 patients with CLL/SLL, 131 (38%) of which were diagnosed in tertiary care centres. Thus, 146 (30%) patients were not known to the provincial cancer registry. Median age of pts was 71 years (range, 24–97). Based on 2001 Canadian census data, the crude incidence of CLL/SLL in Manitoba is estimated to be 7 per 100 000 persons. Other demographic and clinical data of this population-based study will be presented.

Conclusion: By incorporating diagnostic immunophenotyping, the incidence of CLL/SLL appears to be higher than that reported by a large Canadian cancer registry. This observation may apply to other local and national jurisdictions, and should be studied further.