• Chen Wang, Dominick Amato, Rola Rabah, Jianing Zheng, and Bernard Fernandes.
• Department of Pathology and Laboratory Medicine, Mount Sinai Hospital, University of Toronto, Ontario, Canada. cwang@mtsinai.on.ca
• Leuk. Res. 2002 Dec 1; 26 (12): 1125-9.

AbstractChronic lymphocytic leukemia (CLL) is recognized as a unique lymphoproliferative disorder of CD5(+) B cells. However, many published series of CLL included a subgroup of CD5(-) cases. CD5(-) B cell CLL is a topic of controversy and its nature and true incidence remain unclear. We in this study performed a retrospective analysis of a total of 128 consecutive patients with a diagnosis of CLL and available immunophenotypic record. Of these, 14 cases were previously considered CD5(-) CLL. From a further analysis of clinical, hematological and immunophenotypic results, we have reclassified seven of the patients as having weak or dim expression of CD5 and four patients as being monoclonal B lymphocytosis of undetermined significance (MLUS). The remaining three cases had clinical and morphological features consistent with prolymphocytic leukemia (PLL) or mixed CLL/PLL. Our results suggest that the CD5(-) phenotype probably does not qualify for CLL. Previous CD5(-) CLL may include false negatives due to heterogeneity of the intensity of CD5 expression, CD5(-) MLUS and variant CLL; the latter likely represents CLL in transformation. All the patients with MLUS were found to have a mild and non-progressing lymphocytosis with CD5(-) phenotype. These features may be used to differentiate them from CLL.

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