Because hydras have immune systems, telomerase activity, and Piwi-piRNA like cancer cells I wonder if they can get cancer?
Research in cnidarians shows that even pre‐bilaterian animals can develop neoplasia (Domazet‐Lošo et al., 2014). Two different species of Hydra have presented with tumour‐bearing polyps. The cells in these tumours were invasive, which suggests that metastatic capacity has ancient roots. Additionally, the tumours had several orthologues to tumour‐related genes in mammals and displayed parallels to the hallmarks of cancer in vertebrates. The proposed mechanism for tumourigenesis in Hydra is the accumulation of stem cells if they are not appropriately removed by programmed cell death (Domazet‐Lošo et al., 2014). Scientists have also identified several cancer‐like lesions in corals (Aktipis et al., 2015).