Gerson’s central claim, made in his 1958 book A Cancer Therapy: Results of Fifty Cases, was that his regimen could treat cancer even in advanced cases; he reported that about half of his most severe, previously terminal cases could be improved and saved. The claim rested on Gerson’s own selected case histories, not controlled outcome data. The National Cancer Institute reviewed cases from his practice in 1947 and 1959 and found the available information did not prove benefit; no prospective, controlled study of the therapy has been reported in a peer-reviewed scientific journal.