Cancer therapy with phytochemicals: evidence from clinical studies

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Cancer is still one of the major causes of mortality in both developing and developed countries. At this time, in spite of intensive interventions, a large number of patients have poor prognosis. Therefore, the effort for finding new anticancer agents with better efficacy and lesser side effects has continued. According to the traditional recommendations and experimental studies, numerous medicinal plants have been reported to have anticancer effect. Also antiproliferative, proapoptotic, antimetastatic and antiangiogenic effects of several phytochemicals have been shown with in vitro experiments or animal studies. However, only a small number of them were tested in cancerous patients and limited evidence exists on their clinical effectiveness. Also, regarding some phytochemicals, only beneficial effects on cancer-related symptoms or on quality of life have been reported and no positive results exist on their antitumor actions. In this review we focus on phytochemicals that their beneficial effects on various types of cancer are supported by clinical trials. Based our literature search, curcumin, green tea, resveratrol and Viscum album had satisfactory instances of clinical evidence for supporting their anticancer effects. The main findings on these phytochemicals are summarized and discussed.