Quality Evaluation of the Clinical Trials for Natural Products Used in Cancer: An Evidence-Based Literature Review

The amount of data regarding the use of herbs/herbal products in cancer clinical trials at times creates a great challenge for oncologists to prescribe or counsel patients. It urges critical evaluation of the quality of clinical trials. Herein, for the first time, the clinical trials for herbs used in cancer were critically evaluated on the basis of three widely used scales, i.e., Jadad, Delphi, and Cochrane scales. The literature was collected with the help of online databases, journals, libraries, and books using a number of specific keywords as mentioned in detail in forthcoming sections. A total of 73 clinical trials were extracted, evaluated, and scored for 14 herbs, according to the predefined criteria mentioned below. A major deficiency of “non-blinding of clinical trials” was observed. The principal component analysis revealed four components (PC1–PC4) with a total variability of 68.21%, wherein the highest percentage variability was observed for PC1 loaded with “non-blinding of the clinical trials, no concealment of the treatment allocation, non-blindness of the patient and care provider”, which accounted for 30.81% of the total variability. The next major variability of 14.70% was observed for PC2 loaded with “non-randomization of the studies, non-blinding of the outcome assessors, no proper drop-out procedures, and lack of information regarding baseline characteristics for the groups”. Pearson’s correlation further confirmed a similar correlation pattern for the mentioned deficiencies (p = 0.05). An in-house grading scale was developed, showing a very small portion (16.44%), i.e., 12/73 studies with a good quality, whereas the majority (57.54%) of the studies, i.e., 42/73, were found to be of poor quality. The rules and regulations governing the quality of clinical trials needs to be more stringent and updated for the natural products/herbs used in cancer clinical trials.