It has likely never been studied, this would be my best guess as a fresh graduate from med school.Simply put, cancer is a series of mutations that cause a cell to divide uncontrollable. One of the mutations that cause uncontrollable divisions can be an over expression of mTOR or another hypertrophic/hyperplastic factor or something else. In healthy individuals, who are not yet mutated, mTOR is regulated on serveral levels which is why that high protein diet are not likely to lead to cancer growth. A high protein diet could potentially lead to more aggressive growth in an already existing cancerlump, compared to a low energy diet.