I could only find one good 2020 study showing that cannabis treats breast cancer. However, I noticed a suprisingly nice pattern emerging...

There are several studies from 2012 to present showing that Cannabidiolic Acid aka CBDA, the acidic precursor of cannabidiol, (CBD) treats breast cancer, and inhibits cell migration of the highly-aggressive, triple-negative breast cancer MDA-MB-231.

Previous studies have found it works through the down-regulation of cyclooxygenase-2 (COX-2) and c-fos as well as interfering with AP-1 transcription. Current research shows that CBDA inhibits differentiation of ID1, a gene whose up-regulation is associated with cancer metastases and solid tumor growth.

• Zhao Z, Bo Z, Gong W, Guo Y (2020). Inhibitor of Differentiation 1 (Id1) in Cancer and Cancer Therapy. Int J Med Sci. 2020 Apr 6;17(8):995-1005.">2020

• Pellati F, Borgonetti V, Brighenti V, Biagi M, Benvenuti S, Corsi L (2018). Cannabis sativa L. and Nonpsychoactive Cannabinoids: Their Chemistry and Role against Oxidative Stress, Inflammation, and Cancer. Biomed Res Int.

• Suzuki M, Takeda S, Okazaki H, Watanabe K, Takiguchi M, Aramaki H (2017). Cannabidiolic Acid-Mediated Interference with AP-1 Transcriptional Activity in MDA-MB-231 Breast Cancer Cells.Nat Prod Commun. 12(5):759-761.

• Takeda S, Himeno T, Kakizoe K, Okazaki H, Okada T, Watanabe K, Aramaki H. (2017). Cannabidiolic acid-mediated selective down-regulation of c-fos in highly aggressive breast cancer MDA-MB-231 cells: possible involvement of its down-regulation in the abrogation of aggressiveness. J Nat Med. Vol 71(1) Pp. 286-291.

• Takeda S, Okazaki H, Ikeda E, Abe S, Yoshioka Y, Watanabe K, Aramaki H. (2014). Down-regulation of cyclooxygenase-2 (COX-2) by cannabidiolic acid in human breast cancer cells.

• Takeda S (2013). Medicinal chemistry and pharmacology focused on cannabidiol, a major component of the fiber-type cannabis. Yakugaku Zasshi. Vol. 133(10) Pp. 1093-101. Review.

• Takeda S, Okajima S, Miyoshi H, Yoshida K, Okamoto Y, Okada T, Amamoto T, Watanabe K, Omiecinski CJ, Aramaki H (2012). Cannabidiolic acid, a major cannabinoid in
  fiber-type cannabis, is an inhibitor of MDA-MB-231 breast cancer cell migration. Toxicology Letters. Vol 214(3) Pp. 314-9.