Buchheim et al. (2020) demonstrate that cosmonauts’ IgM repertoire differs from that of control subjects before launch and that two of the five examined cosmonauts’ IgM repertoires change over a long-term mission on the ISS (Buchheim et al., 2020). A wide spectrum of biochemical markers (cytokines and chemokines) associated with inflammation, cell growth, and proliferation, as well as tumor proliferation and vascularization, increased during flight and considerably decreased upon return (Vallet et al., 2011; Amarasekara et al., 2018; Yano et al., 2005; Garret-Bakelman et al., 2019). This evidence concerns the gene CD40LG and neoplasm.