Viscum album has been employed traditionally to treat various ailments including as add-on therapy for cancer treatment. V. album formulations have been employed as adjuvants in cancer treatment due to their immunomodulatory activities as well as to alleviate the side effects of conventional cancer therapies. The present review provides updated information from the past 10 years on the immunomodulatory activity and inhibitory effects of V. album on cancer cells, its safety profile, and recent nanotechnology development. V. album extracts and their bioactive phytochemicals, particularly lectins, viscotoxins, and polyphenols, have demonstrated immunomodulatory activity and inhibitory effects against various types of cancer, with low cytotoxicity and side effects, in experimental studies and demonstrated promising anticancer activity in clinical studies in cancer patients. V. album extracts have been shown to enhance immune function by
promoting cytokine secretion and inducing both innate and adaptive immune responses, which can help improve immune surveillance against cancer cells. The development of V. album nanoparticles has boosted their biological activities, including inhibitory activity on cancer cells, and could possibly reduce undesired side effects of the plant. Further prospective studies on the plant as a source of new medicinal agents for use as an adjuvant in the treatment of cancer must be performed to provide sufficient efficacy and safety data.