Multiple endogenous retroviruses (ERVs) in human DNA may be programmed to activate as cancer therapy. A recent study, led by scientists at the Dana-Farber Cancer Institute, expanded on a previously reported case of kidney cancer cure after hematopoietic stem cell transplantation attributed to the expression of an ERV driven by the hypoxia-inducible factor 2 (HIF2). The question was whether this finding might play out with different ERVs and different types of cancer through HIF.