To dream that you have this disease does not have to be a prediction (although if you have symptoms of discomfort, it is worth a check). Cancer is a tumor, and the dream could mean that an undesired element is becoming part of yourself or is growing in excess; for example a growing obsession that can affect your personality, and even your health. Having cancer in dreams also indicates that you do not properly deal with your emotions which end up being destructive; the dream is a warning against that.