Ki-67 Labeling Indices in ‘Classic’ versus ‘Blastoid’ Mantle Cell Lymphomas - Proposed Cutoff Values for Routine Diagnostic Workup

Background: Mantle-cell lymphoma (MCL) is a unique entity of peripheral B-cell lymphoma that has a discretemorphologic, immunologic, and genetic phenotype, with more common ‘classic’ and less frequent ‘blastoid’and ‘pleomorphic’ variants, associated with an aggressive clinical course. The aim of this study was to analyzeproliferation (Ki-67) indices of ‘classic’ (c-MCL) and ‘blastoid’ (b-MCL) variants of a cohort of MCL and tosuggest cut off values for the Ki-67 proliferation index in these two subsets. Materials and
Methods: MCL casesdiagnosed over 4 ½ years at Section of Histopathology, Department of Pathology and Laboratory Medicine,Aga Khan University Hospital, Karachi were retrieved and reviewed. Ki-67 labelling was scored and analysed.
Results: A total of 90 of cases of MCL were scrutinized. Mean age ± SD was 60.2 ± 12.5 years and the male tofemale ratio was 4:1, with 67 (75%) cases of c-MCL and 23 (25%) cases of b-MCL. Most samples were lymph nodebiopsies (n=68), whereas the remainder were from various extranodal sites The mean Ki-67 proliferation indexwas 29.5% ± 14.4% in classic variants and 64.4 ± 15.2% for the blastoid variant, the difference being statisticallysignificant (p = 0.029).
Conclusions: It was concluded that differential cut-off values of Ki-67 labeling may beused in more objective way to reliably classify MCL into classic or blastoid variants by diagnostic pathologists.We propose a < 40 proliferative index to be suggestive of c-MCL and one of > 50 for the blastoid variant.