CAN STRESS CAUSE CANCER?

I firmly believe so! If a person takes care of their body by exercising and eating properly yet is constantly in a high state of stress, it can put quite an impact on your body and mind.
Think of the last time you were really stressed. How did it affect you personally? Did you eat too much junk food, eat too little food in general? Get too little sleep?
These are things people do when they are stressed. And if someone is constantly stressed, it can take a toll on your body and definitely damage your organs, making you prone to cancer. Unless you can control your stress, great, you should be pretty healthy. Otherwise, yes uncontrolled stress can cause cancer.
Breathing exercises and yoga help my stress.

No, it can't. Cancer is caused by DNA damage in individual cells that turn off programmed cell death and cancer suppression genes.
Stress does not cause DNA damage, no matter how stressed you may be. None of the stress-released or releasing hormones can manipulate DNA or the structures in your cells that regulate its formation.

There have been a few studies into this, bt nothing conclusive.
Some theorise that stress in itself can cause cancer, others that stress affects hormone levels so affects hormone driven cancers, stress affects the immune system affecting cancer and others that stress affects alcohol and cigarette intake affecting cancer.
Personally, have heard many anecdotal stories relating a major stress event to cancer a few years later.