I've had two breathwork teachers that cured themselves of cancer simply through conscious breathing. They were the creators of rebirthing and transformational breath. Holotropic breathwork is very similar. The practice involves deep and fairly rapid breath for extended periods of time. And the increased levels of oxygen in the body is said to kill the cancer.
So I just googled breathing to cure cancer so I can share some links here. What came up most was a practice I have not heard of by a Russian doctor named Buteyko. At first glance I thought this looks right in alignment with the other practices. But I was quickly surprised to find out the assertion was that people are actually breathing too much. That over-breathing reduces oxygen levels in the blood. I have known for some time that there is an integral balance between oxygen and CO2 in the respiration process. But this takes it to another level.
So I'm not quite sure what to think. I also found an article disputing the science and theory of Buteyko. But what does seem generally agreed upon is that cancer and oxygen don't mix. Hydrogen peroxide and baking soda treatments are also based on oxygenating the cancer. But those would be a little more invasive if there is a way to do it naturally through our own breath.
Below are a couple quotes from the Amazon listing
Doctors Who Cure Cancer...
"In the 1920s Otto Warburg won the two Noble Peace Prizes for his research conclusions that cancer is caused by a lack of oxygen to body. His "Warburg Effect" have been reaffirmed by more recent research see PubMed."
"Since over 150 Soviet and Russian doctors applied the Buteyko breathing technique on more than 50,000 of their patients, they noticed that early stages of cancer naturally disappear, if their patients improved their body oxygenation up to the medical norm.
These clinical observations resulted in an unique clinical trial on cancer patients organized by one of the Ukrainian physicians who applied the Buteyko method on 120 people with metastatic cancer.
The book "Doctors Who Cure Cancer" provides detailed analysis of the method since this is the most successful clinical trial in the whole history of cancer research. The tested cancer therapy was based on breathing retraining or teaching patients how to breathe in accordance with medical norms days and nights."
http://www.normalbreathing.com/diseases-cancer.php
https://www.sciencebasedmedicine.org/buteyko-breathing-technique-nothing-to-hyperventilate-about/
http://drleonardcoldwell.com/2015/05/28/the-root-cause-of-cancer-and-why-has-it-been-kept-a-secret/
Dr. Warburg has made it clear that: the root cause of cancer is oxygen deficiency, which creates an acidic state in the human body. Dr. Warburg also discovered that cancer cells are anaerobic (do not breathe oxygen) and cannot survive in the presence of high levels of oxygen, as found in an alkaline state.
http://www.medicaldaily.com/breathing-extra-oxygen-shows-promise-fighting-cancer-and-boosting-immune-system-will-324646
http://www.cancer-treatment-tips.com/breathing.html