Gerson's book  and articles in English [2,3,4] are primarily reports of the details of the Gerson regimen, supplemented with case reports of patients seen in his clinical practice. His book presents an extended discourse on the empirical and scientific foundation for his treatment regimen and an expansive description of the treatment and diet followed by 50 patients selected from 30 years of clinical practice. Gerson's published cases encompass a variety of cancer types. The reports are extended case notes, with occasional x-rays of the patients over time. Although some attempt at follow-up is made, it is not systematic and consists chiefly of anecdotal reports and conversations with patients by mail or phone.
A preliminary study conducted between 1983 and 1984 attempted to collect any available retrospective data on three nonallopathic treatments offered in clinics in Tijuana, Mexico: Gerson, Hoxsey, and Contreras. The authors did not have access to medical records and relied on patient interviews for all information. The self-reporting was incomplete and inconsistent, lacking precise information in areas such as how far the disease had advanced. In the Gerson segment, only 18 of the 38 patients stayed in the study for 5 years or until they died; their mean survival was 9 months from the beginning of the study. The other 20 patients were lost to follow-up. At 5 years, 17 of the 18 had died, and one patient with advanced non-Hodgkin lymphoma was alive but not disease free. Overall, this study did not offer meaningful data to support the clinical efficacy of the approaches studied.
The PDQ editorial boards use a ranking system of levels of evidence to help the reader judge the strength of evidence linked to the reported results of a therapeutic strategy. For any given therapy, results of prevention and treatment studies can be ranked on each of the following two scales:
Strength of the study design.
Strength of the endpoints.
Together, the two rankings provide a measure of the overall level of evidence. Screening studies are ranked on strength of study design alone...
A 1990 noncontrolled, self-selected, matched-pairs study conducted in Austria used a diet regimen based on the Gerson therapy to evaluate diet as an adjuvant to surgery. This diet was ovolactovegetarian. The Gerson regimen is basically strictly vegetarian (no eggs or milk) and does not introduce food other than buttermilk until 6 or 8 weeks into the regimen, if at all, depending on the patient.
Two groups of patients who had undergone surgery—18 patients with colorectal cancer with metastases to the liver and 38 with breast cancer —were treated. Each of the two groups was divided into a diet group and a nondiet group. All patients continued with whatever prescribed conventional regimen was required after their surgery. Results in the matched pairs with colorectal cancer showed an increased survival time in three of the nine patients in the diet group (28.6 months) as compared with four of the nine patients (16.2 months) in the nondiet group. In the breast cancer matched pairs, side effects of chemotherapy and pain and pleural effusion were lower in the diet group. No statistically significant information was generated in this small number of patients; however, the authors stated that the diet regimen appeared to have beneficial effects that required further study.