This meta-study covered cancer research involving cannabinoids between 1970 and April 2021. It was published in the Journal of Cancer Research & Clinical Oncology in July 2021. This paper includes and summarizes most of the major research on cannabinoids and cancer over the last 50 years.
The best summary of this research is probably from the authors themselves.
"Phyto-, endogenous and synthetic cannabinoids demonstrated anti-tumor effects both in vitro and in vivo. However, these effects are dependent on cancer type, the concentration and preparation of the cannabinoid and the abundance of receptor targets."
"Cannabinoids have shown to be efficacious both as a single agent and in combination with antineoplastic drugs. These effects have occurred through various receptors and ligands and modulation of signalling pathways involved in hallmarks of cancer pathology."