Unfortunately, changing telomerase activity is also rather strongly linked to cancer. Still, with the dramatic improvements in cancer treatment over the last 30 years there may be a useful tradeoff where an increased cancer risk is offset by an increased heath / lifespan on average. But, don't expect a free lunch as evolution tends to find those fairly quickly.
This study "shows that it is possible to develop a telomerase-based anti-aging gene therapy without increasing the incidence of cancer," the authors affirm.
Translation: "There was no statistically significant increase in cancer detected." However, that's less meaningful than you might think as detecting even a 2x increase in cancer among mice is a lot harder than say showing in increased population lifespan.
The real question is what was their power to detect an X-fold increase in cancer. Probably quite low, as that was not the purpose of this particular study.
