In our opinion, future studies should clarify whether endocan can be used as a predictive/prognostic biomarker for severe cytokine-mediated reactions not only in COVID-19 infections but also in acute leukemia patients receiving immunotherapy or being at risk of severe immune-mediated toxicity (i.e., haploidentical transplantation, checkpoint inhibitor or CAR-T cell therapy, bispecific antibody treatment) that may require prophylactic, early systemic, or strengthened immunosuppression [113,117,118]. Here, ESM1 is linked to acute leukemia.