Multiparameter immunohistochemical analysis of the cell cycle proteins cyclin D1, Ki-67, p21WAF1, p27KIP1, and p53 in mantle cell lymphoma.

BACKGROUND

Mantle cell lymphoma (MCL) is characterized by overexpression of cyclin D1, a G1 cyclin that participates in the control of cell cycle progression at the G1 to S phase transition. In addition to cyclin D1, other cell cycle regulatory molecules may be involved in the proliferation and progression of MCL. Mutation of p53, deletion of p16(INK4a), and loss of p21(WAF1) expression have been reported in some cases of blastoid MCL.

OBJECTIVE

We sought to examine levels of expression of these proteins in typical and blastoid MCL and to determine whether differences were present between these subtypes of lymphomas.

DESIGN

A retrospective series of typical and blastoid MCLs was evaluated for expression of the cell cycle-related proteins cyclin D1, p21(WAF1), p27(KIP1), Ki-67, and p53, as well as mitotic index. Paraffin-embedded archival tissues from 24 MCL specimens (17 typical, 7 blastoid) were immunostained with antibodies to p21(WAF1), p27(KIP1), p53, Ki-67, and cyclin D1. The percentage of positive cells for each specimen was estimated by counting 1500 cells under oil immersion microscopy. Levels of antigen expression were compared for the typical and blastoid MCLs. The mitotic index was estimated using twenty 100x oil immersion fields (OIFs) for each specimen.

RESULTS

Cyclin D1 expression was seen in 22/24 specimens (92%). Blastoid MCLs were characterized by a significantly higher mean mitotic index (>20 mitoses/20 OIFs) and Ki-67 index (>45%) when compared with typical MCLs (P <.001 and P <.008, respectively; Fisher's exact test). High expression of p27(KIP1) (>25% staining) was seen more frequently in typical MCLs than in the blastoid variants (P =.03; Fisher's exact test). No significant differences were found between typical and blastoid MCLs for the expression of p21(WAF1) or p53.

CONCLUSIONS

A significantly higher mitotic index and Ki-67 index were found in blastoid MCLs as compared with typical MCLs. Low p27(KIP1) expression was associated with the blastoid MCL variant. These findings confirm the high proliferative nature of blastoid MCL and suggest a role for p27(KIP1) in the negative regulation of the cell cycle in MCL.