This is a review study specifically focused on cannabinoids and their effect on breast cancer published in the journal Molecules in December 2021. The authors state that "cannabinoids are promising therapeutic agents for the different breast cancer subtypes, being able to exert important actions on cell survival and metastasis."
However, they also state that cannabinoid effectiveness is dose-dependent and even biphasic - in this case meaning it can promote growth at low doses, and inhibit growth at higher doses.
"This biphasic behavior is correlated with the cannabinoid concentration used, since lower concentrations seem to induce cell proliferation and survival, while higher doses are associated with cell death and inhibition of cell growth."
In many of the positive studies we have reviewed, the daily doses were well above a standard recreational dose, in the range of 500mg and more of each cannabinoid.
They found studies on many cannabinoids (including synthetic) including THC, CBD, CBG, CBN, CBDV.
The full text paper here is at MDPI.com.