The idea that cannabis can fight or kill cancer cells stems from promising preclinical studies in laboratories and animal models, where specific cannabis compounds (cannabinoids) have shown anti-tumor effects. These findings have not yet been confirmed in large-scale human clinical trials, and there is currently no convincing evidence that cannabis can cure cancer in humans.

Basis of the Anti-Cancer Claims Laboratory and animal studies have indicated that cannabinoids like Δ⁹-tetrahydrocannabinol (THC) and cannabidiol (CBD) can influence cancer cells through several cellular mechanisms.

Inducing Cell Death (Apoptosis and Autophagy): Cannabinoids can trigger programmed cell death in cancer cells while often sparing healthy, non-transformed cells. This process often involves the modulation of the endocannabinoid system (ECS) within the cancer cells, leading to cellular stress responses in the endoplasmic reticulum (ER) and the production of a pro-apoptotic lipid called ceramide.

Inhibiting Cell Proliferation: Cannabinoids have been shown to stop the uncontrolled growth and division of cancer cells by arresting the cell cycle in various cancers, including breast, lung, and prostate cancer cell lines.

Reducing Angiogenesis: They can impede the formation of new blood vessels that feed tumors (angiogenesis) by blocking pathways such as the vascular endothelial growth factor (VEGF) pathway.

Blocking Invasion and Metastasis: Studies suggest that cannabinoids can reduce the ability of cancer cells to migrate and spread to other parts of the body (metastasis). This effect is partly due to the downregulation of enzymes like matrix metalloproteinases (MMPs) which break down tissue.

Important Considerations and Current Status
While the preclinical results are encouraging, several critical points remain:
Lack of Human Clinical Evidence: To date, research has primarily involved cell cultures and animal models. Large, well-designed human clinical trials proving that cannabis can effectively treat or cure cancer are still needed and are a focus of ongoing research.

Palliative vs. Curative: Cannabinoid-based medicines are currently approved in some regions for managing cancer-related symptoms, such as nausea, vomiting, pain, and appetite loss, not for cancer treatment itself.

Potential Negative Interactions: In some specific circumstances, cannabinoids have been shown to potentially promote tumor growth or interfere with standard cancer therapies, highlighting the complexity of their effects and the need for medical supervision.

In summary, the scientific community is actively investigating the anti-cancer potential of cannabinoids, but medical professionals and organizations like the National Cancer Institute caution that cannabis is not a proven standalone cancer treatment at this time.