When Elon Musk unveiled SpaceX's plans for sending humans to Mars in September 2016, he had a remarkably cavalier attitude towards the dangers of space radiation. There's going to be some risk of radiation, but it's not deadly," he told the audience in Guadalajara, Mexico back then.
There will be some increased risk of cancer, but I think it's relatively minor. The radiation thing is often brought up, but I think it's not too big of a deal. The study was published in the journal Proceedings of the National Academy of Sciences.