This was exactly Dr. Max Gerson's theory -- that cancer patients have too much sodium and too little potassium. And not only cancer patients -- he believed this imbalance underlies most chronic health conditions and diseases. Gerson is far more credible to me than most because his many cures of tuberculosis (including Albert Schweitzer's wife's TB in the days before antibiotics), auto-immune diseases and cancer are meticulously documented and have withstood the withering scrutiny of mainstream docs.
He corrected it with diet, LOTS of freshly-pressed vegetable and apple juices, fortified with a potassium compound of his creation that consisted of 3 potassium salts , and a detox program. He said it took a long time to get the sodium out of the cells and replace it with potassium.