PRDM1 (PR domain zinc finger protein 1) is a transcription factor critical for cell fate determination and terminal differentiation. It plays a pivotal role in B cell development, driving mature B cells into antibody-secreting plasma cells while repressing B cell identity genes. Beyond immunity, PRDM1 regulates differentiation in other lineages, such as T cells and epithelial cells, and acts as a tumor suppressor in multiple cancers by inhibiting cell proliferation and inducing apoptosis. Dysregulation of PRDM1 is linked to lymphoid malignancies (e.g., multiple myeloma, diffuse large B-cell lymphoma) and solid tumors.