Systemic assays conducted with various B‐cell lymphoma cell lines and a mouse xenograft model demonstrate that the non‐phosphorylation variant of CARF inhibited cell proliferation and lymphoma formation more effectively than wild‐type CARF, highlighting the crucial regulatory role of phosphorylation at these conserved sites in controlling B‐cell lymphoma cell proliferation. Here, CARF is linked to B-cell non-Hodgkin lymphoma.