Purpose of Review <p>It is important for physicians to understand the late effects of chimeric antigen receptor T-cell (CAR T) therapy because more cancer survivors are presenting to the emergency department (ED) months to years after treatment, often with atypical or life-threatening complications. CAR T therapy, used for hematologic malignancies such as diffuse large b cell lymphoma, B cell acute lymphoblastic lymphoma, mantle cell lymphoma and multiple myeloma. As CAR T use expands, ED clinicians will increasingly encounter these patients, making familiarity with long-term complications an essential component of emergency care.</p> Recent Findings <p>One major concern is prolonged cytopenias and hypogammaglobulinemia, which increase the risk of severe or opportunistic infections. Physicians must recognize that fever in a patient who has previously received CAR T may represent overwhelming sepsis even in the absence of typical inflammatory responses. Early appropriate antibiotic administration and rapid evaluation are critical.</p> Summary <p>CAR T therapy alters immune function in complex and sometimes prolonged ways, awareness of its late effects improves diagnostic accuracy, prevents delays in life-saving treatment, and reduces morbidity and mortality both in the ED and in the hospital.</p> Abstract <p> Chimeric antigen receptor CART -cell therapy has revolutionized the treatment of hematologic malignancies, achieving unprecedented response rates. However, the long-term effects of this powerful immunotherapy are increasingly recognized as a critical aspect of patient care. This review explores the late effects of CART -cell therapy, focusing on hypogammaglobulinemia, prolonged cytopenias, and late infections, encompassing bacterial, fungal, parasitic, and viral etiologies. Additionally, this review will discuss ways in which these conditions can be treated in an acute care setting.</p>