Technically, a ~1,000 day mission to Mars (including ~500 days spent on the planet's surface) would entail about 1 Sievert of radiation. That's only a death sentence if you're getting it within a very short period of time, but it's quite survivable when spread out over the given timeframe. While there would be an increased tumor risk over the remaining lifetime of a Martian astronaut, it would be far from a guarantee.

However, that given radiation figure does not include the use of shielded habitats or spacecraft. If need be, local dirt could provide very effective protection, but radiation exposure on the surface of Mars is less of a problem relative to that encountered in deep space. For that, there are promising, lightweight albeit bulky materials that could provide a significant risk in radiation absorption. Some people have also suggested the use of reusable shields or shielded Aldrin cyclers in perpetual transfer orbits: The idea being that interplanetary vehicles would 'dock' with these structures after burning towards Mars.