Pollutants are a definite catalyst for diseases such as cancer. Everyone reacts differently, however. If two people who are exposed to the same amount of pollutants, one could be more genetically predisposed to develop cancer over the other. There is no way of knowing so cutting down the amount of pollutants in your life is always a good idea.
You should stop worrying. The subconscious mind is powerful and the negative thoughts could be making it worse.
Take care of yourself and get regular check-ups if you are worried. I have cancer, very early stages mind you, but I am functioning normally in every day like. If I let the idea of cancer scare me, I would wrap myself in a bubble and not come out...but what fun would like be then??