Highly processed white flours
The EPA states that chlorine gas is a dangerous irritant that is not safe to inhale and in large quantities can be lethal. White flour lurks in many processed foods. White processed flour has a very high glycemic rate which quickly raises the blood sugar level and insulin levels, which can be a direct cause of diabetes, not to mention it is believed that it spreads cancer cells by feeding the cells directly.
Cancerous tumors feed mostly on the sugars in your bloodstream. By avoiding refined grains such as white flour, you can avoid, or at the very least, starve tumors.