This study includes adults with multiple myeloma or B-cell lymphoma who were/will be treated with CAR-T cell therapy at the IRCCS Azienda Ospedaliero-Universitaria di Bologna. The aim is to better understand infections that may occur during the first year after CAR-T treatment, including how often they happen, their causes, and factors that may increase the risk. The study will use information from patients treated in the past and from newly enrolled patients. For some patients who develop fever after CAR-T therapy, a rapid molecular blood test will be used alongside standard tests to help identify bloodstream infections more quickly and support timely clinical care.