RB1 is inactivated in primary MCL. (A) Three of 8 PCR fragments designed to amplify the full-length RB1 cDNA are shown. Fragment 2, involving exon 2, 3, 4, and 5, amplified from a primary MCL (MCL 577), was shorter than the one amplified from the control (C+). (B) Genomic DNA from this primary MCL (MCL 577) and normal tissue (C+) were used in a multiplex PCR reaction in order to amplify exon 2, 3, 4, and 5 of RB1 together with β-actin. Only exons 2 and 5 were amplified in the primary MCL (MCL 577). (C) Immunohistochemical analysis of pRB1 in the primary tumor (MCL 577). A number of normal cells were positively stained (inset), but the tumor cells were negative.