A carcinogenic parasitic worm could do a lot of good one day. Michael J Smout of James Cook University in Queensland, Australia, and colleagues were looking at the oriental liver fluke Opisthorchis viverrini, which infects around 10 million people in Thailand and Laos who pick it up from eating contaminated raw fish. The parasitic worm can stay in the host’s liver for decades, eating the liver but, it seems, patching it up with growth-factor Ov-GRN-1, which it secretes as it goes along. This keeps the host alive until the cumulative damage and inflammation causes bile-duct cancer, resulting in 26,000 deaths per year. The upside is that Ov-GNR-1 accelerates healing and blood-vessel growth in mice, and holds promise for helping the impaired healing of diabetic and elderly patients. Understanding it may also lead to a vaccine for people who have the parasite.