As a further test of the hypothesis that aSHM generated mutations of the CCND1 locus are driving CCND1 mRNA expression levels and that CCND1 is a rate-limiting factor for MCL lymphomagenesis, we analyzed the spectrum of coding mutations in the first exon of CCND1. The first exon as part of the CCND1 transcription regulatory region is potentially subject to selection pressure at the level of transcription as well as protein function. Here, CCND1 is linked to mantle cell lymphoma.