This systematic review focuses on evaluating the overall effectiveness and side effects of CAR T-cell therapy in the treatment of relapsed or refractory DLBCL, with a focus on understanding the factors that affect clinical outcomes and the development of treatment-related toxicities, which include tumor microenvironment, tumor burden, circulating monocytes, single nucleotide polymorphism in CD19, PPM1D gene mutation, and delayed drug infusion [4-6]. The gene discussed is PPM1D; the disease is diffuse large B-cell lymphoma.