MKI67 and B-cell chronic lymphocytic leukemia: Indeed, CLL cells circulating in the PB are quiescent and arrested in the G0/G1 phase of the cell cycle, whereas those residing in the proliferation centers express markers of cell proliferation and DNA replication such as Ki67 [6], cyclin D1 [7,8], and cyclin D2 [9], and phosphorylation of the minichromosome maintenance 2 (pMCM2) [10].