Chronic lymphocytic leukemia in a Japanese population: varied immunophenotypic profile, distinctive usage of frequently mutated IGH gene, and indolent clinical behavior

Abstract

Chronic lymphocytic leukemia (CLL) is relatively rare in Japan. Among 46 cases of mature B-cell leukemia, we identified 28 Japanese patients with CLL, including prolymphocytoid and lymphoplasmacytoid morphological variants. Compared with Western patients with CLL, only 52.0% of cases showed the typical immunophenotypic profile. IgG-bearing (15.4%) and clearly CD20-expressing (71.4%) cases were frequently observed. Most cases harbored a mutated immunoglobulin heavy-chain (VH) gene (88.5%) and commonly used a VH3 family member (61.5%) other than VH3-21. During the median follow-up period of 64 months, 20 cases (71.4%) showed an indolent clinical course without any treatment, and six cases (21.4%) were accompanied by other malignancies. Binet A stage (p = 0.003), low-risk category according to the modified Rai classification (p = 0.016), and ≤ 15 U/mL level of serum thymidine kinase activity (p = 0.016) were associated with prolongation of treatment-free status. Although Japanese cases of CLL showed heterogeneity in morphology and immunophenotype, most cases arose from post-antigen-selected B cells and presented with indolent clinical behavior.

Keywords:

• Chronic lymphocytic leukemia
• immunophenotype
• VH usage
• thymidine kinase activity

Acknowledgements

The authors would like to thank Dr. Makoto Sasaki, Dr. Jun Ando, Dr. Naoko Inagaki, and Dr. Yuko Yamamoto for their assistance in collecting clinical data.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.