IL6 and macrophage activation syndrome: As COVID-19 severity correlates with hyperactivation of the immune system, typified by MAS, lymphopenia, endothelial dysfunctions, and immunothrombosis (18), we first assessed the expression of biomarkers of COVID-19 severity, such as IL-6, CRP, and D-dimer (1, 19, 20), in the plasma from COVID-19-only (COV) (n=50) vs COVID-19 cancer (COV/CA) patients (n=25) (Table 1; Supplemental Table 4).