Cancer is a group of various diseases, all of which involve unregulated cell growth. Many currently used chemotherapeutic drugs are derived from botanicals. Thus, searching botanical sources for novel oncology medications, including identifying the lead compounds and their derivatives for chemoprevention, is an essential step in advancing cancer therapeutics. This article mainly focuses on the data from our previous American ginseng anti-colon cancer studies. In addition to the potential role of American ginseng on cancer, the herb as an adjuvant for cancer treatment is presented, including describing the attenuation of adverse events induced by chemotherapeutic agents and increasing of quality of cancer patient life. Since heat-treated American ginseng and ginsenoside gut microbiome metabolites showed significant increases in cancer chemopreventive effects, active constituents of the steamed herb and their gut metabolites should be clearly identified, and the structure-activity relationship should be further explored. Data obtained from herbal medicine studies and clinical trials will help develop useful anticancer agents.