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.
Our brain can remember loads of images we see everyday. These images are stored by a part of the brain. When we are reminded of the incident or the person, our brain reproduces these related thoughts in the form of images. Some people with extra sensory perception experience dreams about future. They can predict the future through their dreams. To experience a pleasant dream, always go to sleep with positive thoughts. These thoughts not only induce good dreams but also give you a fresh start in the morning.