Along this principle, we have identified a CLL patient with a previously undescribed t(X;14)(q28;q32) translocation, which leads to co-localization of the mature T cell proliferation 1 (MTCP1) coding region with the IGH locus, a situation analogous to the translocation of BCL2. Despite no known role in CLL, we found elevated MTCP1 mRNA expression in CLL cells compared to normal B cells and that increased MTCP1 expression in CLL patients portends poor outcomes to chemoimmunotherapy. Here, MTCP1 is linked to B-cell chronic lymphocytic leukemia.