MDK and plasma cell myeloma: Irradiated breast cancer cells MCF7 exhibited higher cell survival and lesser DNA damage when co-cultured with M2 macrophages [47], which can promote the repair of Double-Strand Breaks (DSBs) in multiple myeloma cells through the non-homologous end-joining (NHEJ) process [48] and induce overexpression of Midkine (MDK), a transcriptional factor involved in the p53-DDR axis [49].