This chapter examines some of the recent evidence‐based scientific information about the contribution of phytotherapeutics for effective cancer management with particular emphasis on results of human clinical trials. It discusses the clinical evidence of effectiveness of phytotherapeutics mainly in relation to the anticancer mechanisms through natural killer (NK) cell enhancement. NK cells play an important role in anticancer immunomodulation. Two commonly used phytotherapeutics, the medicinal mushrooms Lentinula edodes mycelia and Ganoderma lucidum, have been found to elicit their anticancer functions by regulating NK cells. If effects on both NK numbers and toxicity are taken into account, the recommended phytotherapy strategies appear to be Hochu‐ekki‐to, Shenqi Fuzheng Injection (SFI), and Aidi Injection. The chapter highlights the importance of careful documentation of the clinical effects for both overall survival and quality of life, in relation to potential mechanisms of action for further evidence‐based use of selected cancer phytotherapeutics.