Ki-67 labeling indices in \u27Classic\u27 versus \u27Blastoid\u27 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 discrete morphologic, immunologic, and genetic phenotype, with more common \u27classic\u27 and less frequent \u27blastoid\u27 and \u27pleomorphic\u27 variants, associated with an aggressive clinical course. The aim of this study was to analyze proliferation (Ki-67) indices of \u27classic\u27 (c-MCL) and \u27blastoid\u27 (b-MCL) variants of a cohort of MCL and to suggest cut off values for the Ki-67 proliferation index in these two subsets. Materials and Methods: MCL cases diagnosed over 4 1/2 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 to female ratio was 4:1, with 67 (75%) cases of c-MCL and 23 (25%) cases of b-MCL. Most samples were lymph node biopsies (n=68), whereas the remainder were from various extranodal sites The mean Ki-67 proliferation index was 29.5%±14.4% in classic variants and 64.4±15.2% for the blastoid variant, the difference being statistically significant (p=0.029). Conclusions: It was concluded that differential cut-off values of Ki-67 labeling may be used in more objective way to reliably classify MCL into classic or blastoid variants by diagnostic pathologists. We propose a \u3c40 proliferative index to be suggestive of c-MCL and one of \u3e50 for the blastoid variant