BCG not only reacts to tumor cells by activating the immune system, leading to apoptosis, necrosis, oxidative stress etc. On the other hand, BCG can directly act on many cells in the whole tumor immune microenvironment (TME), such as macrophages, neutrophils, T cells, etc., releasing IL-6 and IL-8 cytokines to generate a cascade response to promote the host immune system to kill tumor cells (Figure 1). The gene discussed is IL6; the disease is neoplasm.