Hi Carol,
There are some very mixed messages about this. The widely held view is that a low carb diet increases risk of colon cancer. But research shows this to be true only in cases where the subjects' diets were also very low in fibre. There is also research being done in Würzburg and Tübingen in Germany and in Amsterdam using a zero carb ketogenic diet to reverse cancer tumours. This research is in early stages but has already shown some success.
So, depending on which research you want to follow, low carb causes cancer and low carb cures cancer tumours.