The aim of this observational study was to assess the seroprevalence of IgM/IgG antibodies in cancer patients undergoing systemic treatment at Clinica Oncologica Azienda Ospedaliero-Universitaria Ospedali Riuniti di Ancona—Università Politecnica delle Marche (UNIVPM), as per assessed by rapid and serological tests. Here, CD40LG is linked to cancer.