Even at concentrations of less than 1.3 pCi/L for a non-smoker, for a lifetime exposure, the estimated incidence of lung cancer is 2/1000 which is way higher than the typical acceptable cancer risk for residential exposures to potential carcinogens of 1 per 1,000,000 individuals exposed over a lifetime.

Here is the offical scoop on radon and risk:  https://www.epa.gov/radon/health-risk-radon#head