For years I've read those clickbait headlines proclaiming how "Smoking pot cures cancer." For the most part, these headlines were, at best, stretching the truth, but that's nothing new when it comes to science reporting. Whenever you see a headline that says "A recent study proves…" ignore it immediately because the reporter knows nothing about science. A single study (recent or otherwise) can only suggest until it's been replicated and other research has further confirmed the findings.
The government, via cancer.gov, has however finally made some more conclusive remarks about the often demonized cannabis plant and its properties. Several studies on mice and rats have shown that cannabinoids may inhibit tumor growth. More laboratory and animal studies further showed that cannabinoids may kill cancerous cells while protecting healthy cells. That's not all, a certain type of colon cancer may be inhibited due to cannabinoids anti-inflammatory effect in the colon. This could make cannabis a potential deterrent or even treatment for colon cancers.
The primary active constituent in marijuana is delta-9-THC. This is only one of many cannabinoids, but it's the most well known as it's responsible for the psychoactive effect ("the high" as your garden variety pothead might say). Delta-9-THC damages or even kills hepatocellular carcinoma (liver cancer) cells. In that same study, it was shown to have anti-tumor activity as well. Scientists have extrapolated that THC might be able to act similarly on similar cells such as lung and breast cancer cells.
Cannabidiol (CBD) is a non-psychoactive component of cannabis that has multiple health benefits as well. CBD caused cancer cell death in breast cancer while having little effect on normal breast cells. Even in cases of metastatic breast cancer in mice CBD and other cannabinoids lessen growth, number, and spread of tumors. A meta-review of 34 studies related to cannabinoid effects on glioma tumor models found that in all but one study cannabinoids killed cancer cells without harming healthy cells. A similar laboratory study of CBD in human glioma cells found that when offered alongside of chemotherapy, CBD made the chemotherapy more effective and increased cancer cell death without any ill effect on healthy cells. More studies on the mouse model of cancer also showed that CBD alongside delta-9-THC could potentially improve the efficacy of temozolomide and chemotherapy.
The release from cancer.gov also covers cannabis and the cannabinoids' effectiveness at appetite stimulation, pain management, anxiety and nervous disorders and other conditions.