The essence of secondary hemophagocytic syndrome (HPS) is a severe disease caused by over-activation of the immune system. Viruses, bacteria, and tumors stimulate reactive T cells and monocytes to secrete large amounts of cytokines causing cytokine storm, IFNγ and TNF-α cause myelopoietic suppression, and IFN-γ, TNFα, and IL-1 cause fever, abnormal liver function, hyperlipidemia, and coagulation disorders. The prognosis of HPS is poor, with death in about half of the cases. Those with a fulminant course deteriorate rapidly and die within 4 weeks.