The National Cancer Institute states that cannabis treats a wide variety of disease symptoms and has been shown to kill cancer cells. Research suggests cannabis may exert anti-cancer effects by causing cell death, modulating cell-signaling pathways, and inhibiting tumor invasion. 
A 2011 study of cannabidiol (CBD) found that CBD kills breast cancer cells by inducing endoplasmic reticulum stress and inhibiting cell-signaling. In addition, colon cancer studies show that CBD has a cancer-protective effect and reduces cell proliferation. A 2015-2017 study that dealt with the effects of cannabis on a large population of cancer patients showed that 96% of patients reported a general improvement in their condition. Over a third reported a reduction in medication. There was a significant drop in pain intensity and a decrease in nausea and vomiting.
Many cancer patients find it difficult to manage their pain and suffering, and therefore cancer has for some time been approved by the Israeli Ministry of Health for treatment with medical cannabis, since it has very few if any serious side effects and offers great relief from symptoms.