Differential expression of CKS-1B in typical and blastoid variants of mantle cell lymphoma

Mantle cell lymphoma is a distinct type of B-cell lymphoma characterized by the t(11;14)(q13;q32). Mantle cell lymphomas exhibit a spectrum of morphologic findings, of which a subset of tumors is clinically aggressive with a high proliferation rate. These neoplasms are known as aggressive variants of which there are blastoid and pleomorphic subsets. CKS-1B (CDC28 protein kinase regulatory subunit 1B) is essential for the ubiquitination and degradation of p27 and cell cycle progression. We analyzed CKS-1B expression in mantle cell lymphoma cell lines and tumors by Western blot and immunohistochemical analysis. In 4 mantle cell lymphoma cell lines, CKS-1B was expressed at variable levels and correlated inversely with p27 expression. In mantle cell lymphoma tumors, CKS-1B was positive in 10 (28.6%) of 35 typical versus 14 (87.5%) of 16 blastoid/pleomorphic cases (Fisher exact test, P = .0002). Analyzed as a continuous variable, the percentage of CKS-1B-positive cells significantly correlated with blastoid/pleomorphic morphology (Mann-Whitney U test, P = .001). Twelve (23.5%) of 51 mantle cell lymphoma tumors expressed p27. Proliferation rate (Ki-67) was higher in blastoid/pleomorphic variants than in typical mantle cell lymphoma tumors and was inversely associated with p27 levels in typical mantle cell lymphoma. However, CKS-1B expression did not correlate with p27 expression, proliferation rate, or prognosis in the entire study group. Fluorescence in situ hybridization analysis of 10 CKS-1B-positive mantle cell lymphoma tumors showed no evidence of CKS-1B gene amplification. We conclude that CKS-1B is commonly expressed in mantle cell lymphoma, particularly in aggressive histologic variants, and may be involved in pathogenesis.