Analysis of DNA damage within leukocytes in vivo (via immunostaining for γH2AvD, the Drosophila γ-H2AX equivalent) revealed that DNA damage levels were minimal in nuclei of 18 h APF leukocytes, but significantly increased in nuclei of leukocytes migrating under confinement (Fig. 5K,L; Appendix Fig. S2C); this parallels the increased DNA damage within immune and cancer cells migrating through artificial micron-scale constrictions in vitro (Pragya Shah et al, 2021; Raab et al, 2016). This evidence concerns the gene H2AX and cancer.