How Cannabinoids May Help Treat Breast Cancer | Research and Human Cases | Cannabis For Cancer

Breast cancer is one of the most common cancers in women, and relatively prevalent throughout the United States as a whole. It makes up 15.5% of all new cancer cases and 6.8% of all cancer deaths. Cannabinoids have been extensively studied for their ability to fight hormone receptor-positive and negative breast cancer.

One of the earliest studies to examine cannabinoids against breast cancer was in 2010, when Spanish researchers showed THC could combat the HER2+ type (also known as ErbB2). In animals, THC caused cell death (known as apoptosis), reduced the growth of blood vessels to tumors, and decreased spread to lungs. In the chart here, THC was compared with the control group as well a synthetic cannabinoid called JWH-133, which activates the CB2 cannabinoid receptor in a similar way as THC. As demonstrated, mice in both cannabinoid groups had significantly smaller tumor volume. Also notably, whereas 41% of the control group had 4 or more tumors, 0% of cannabinoid-treated animals had that many.
 

The other major cannabinoid, CBD, has also demonstrates activity against breast cancer cells, with a 2011 study indicating it could induce apoptosis in 4 different cell lines, two being estrogen receptor-positive and the others being estrogen receptor-negative. In agreement with other studies, the experiments here pointed to the dose-dependent nature of CBD, with higher doses leading to more cancer cell death.

Another important CBD study was conducted in 2011 by Dr. Sean McAllister of California Pacific Medical Center, where he demonstrated CBD could reduce tumor volume in animals. Part of CBD’s mechanism was downregulating a gene called ID-1, which is involved in tumor growth. As the charts demonstrate, CBD treatment resulted in lower primary tumor volume and weight, reduced number of lung metastases, and less volume in the metastatic regions.

A particularly extensive study was carried out in 2018 by noted researchers Cristina Sanchez and Manuel Guzman’s team in Spain. The goal was to determine if a whole-plant cannabis extract, known as the cannabis drug preparation (CDP), was superior to isolated cannabinoids. The role of terpenes were also examined, as well as which types of breast cancer the cannabinoids were effective against. The main findings were:

• THC and the CDP effectively reduced viability, or number of living cells, of three breast cancer types – ER+/PR+ (T47D cells), HER2+ (HCC1954), and Triple-negative (MDA-MB-231 and SUM159) cells

• The top 5 terpenes in the CDP were not responsible for the extracts’ enhanced efficacy, pointing to the importance of lesser terpenes, other cannabinoids, or other compounds entirely

• The CDP worked by itself and synergized with various chemotherapeutic agents in three different animal experiments

Interestingly, for the ER+/PR+ and HER2+ cells, the CDP was superior to THC at each dose. However, for the triple-negative cells, the highest doses tested of THC and the CDP had essentially equivalent efficacy. More importantly, the animal studies all showed the CDP was vastly superior to THC alone, and that it generally worked together with chemotherapy to enhance efficacy.

Each mouse study conducted was similar, with an inactive vehicle (white), THC alone (green), the CDP alone (blue), a chemotherapy drug (orange), and the chemotherapy drug combined with the CDP (red). This first chart is for ER+/PR+ generated tumors, and the drug used was tamoxifen. In this case, THC was little more effective than the vehicle, while the CDP was essentially equivalent to tamoxifen. The combination of both was most effective.

The HER2+ mouse study was quite similar, although in this case, the CDP, chemotherapy, and combination efficacies were all very similar. Again, THC alone didn’t do much.

Finally, with the triple-negative mouse study, the chemotherapy alone or chemotherapy + CDP combination was significantly better than the CDP alone.

While results can’t be directly extrapolated to humans, this and other evidence strongly favors the superiority of whole-plant cannabis extracts over isolates.

Several patients have reported experiencing anticancer effects from high doses of cannabinoids. Kat Kytle was diagnosed with Stage IV metastatic triple-negative breast cancer around August 2014, with a prognosis of 18 months to 2 years given the cancer’s extent. She declined chemotherapy and used CBD and THC in numerous forms, including topically, infused oils, and a suppository extract. These treatments alone controlled the cancer for a time. It is unclear if Kate stopped using cannabis at some point, but in any case, she was then diagnosed with HER2+ breast cancer in July 2015. At this point, antibody therapy drugs were added to her protocol, and the tumors were nearly eliminated.
 

Tammy Levent is a Florida resident whose cancer battle was covered by a local affiliate of NBC. She was diagnosed with breast cancer in May 2015, and after a lumpectomy removed some of the cancer, she refused further conventional treatment. She then began using apparently THC-rich extract, and in 2016 was cancer free. Lisa Genovese, a nurse on Tammy’s medical team, stated “When I looked at Tammy’s blood work the tumor markers were all zero – and I couldn’t explain it.” Her physician, Dr. Eduardo Palanca, voiced support for more study into the anticancer effects of cannabis, and noted that existing preclinical research already supports THC’s potential.
 

At the 11th National Clinical Conference on Cannabis Therapeutics in May 2017, Dr. Sean McAllister, who conducted the CBD/ID-1 gene study mentioned earlier in this video, discussed his research and shared a fascinating patient case that had been sent to him. The patient used THC and CBD alongside chemotherapy to achieve dramatic reduction of metastatic breast cancer in just 4 months. As the images show, the regression is quite striking and was apparently unexpected with chemotherapy alone. As of this video’s production it is now 2025, and I am less than a week away from attending the 16th incarnation of this same conference.
 

Lin Coxon, a resident of Derbyshire, England, was diagnosed with breast cancer on June 28, 2017. She had a 33mm breast tumor and metastasis to lymph nodes. While awaiting chemotherapy, scheduled in August, she began taking CBD oil to see it would help. By July 24, she could no longer feel the tumor, leading her to get another scan. This revealed the tumor had shrunk to 11mm, and the lymph node metastasis had also decreased tremendously. She then deferred chemotherapy, and using just CBD, beat back the cancer.
In 2020, a smaller amount of cancer returned. Lin tried chemotherapy this time, but couldn’t tolerate it and barely used any. She also had surgery, where a small 1mm nodule of cancer was removed from her breast, along with 5 lymph nodes, of which only 1 was cancerous. Overall, these treatments combined with CBD oil beat the cancer yet again, and as of 2022 Lin was completely cancer free.
 

A report from the Oklahoma station News9 shared Rhonda Gossett’s story of fighting cancer with conventional therapies and cannabis. She initially used just conventional therapies and surgery for metastatic breast cancer, which were successful and kept it at bay for several years. After it returned more aggressively, and conventional therapies were ineffective, Rhonda was told nothing more could be done. At this point, she went to Colorado to use THC oil. Rhonda said she started feeling better soon after starting it, and within a few weeks, scans were showing reductions in her brain metastases. The therapy successfully eliminated the cancer, apparently on its own, within 2 years.
 

Sharon Letts, an accomplished cannabis journalist, was diagnosed with lobular carcinoma breast cancer in 2012. She started on THC extract shortly after diagnosis, which quickly led to symptomatic relief including better sleep. After two and a half months, Sharon was cancer free, having not used any surgery, chemotherapy, or radiation. As of 2025, she is still doing very well. Sharon has had quite a remarkable life, and the picture here shows her with actor and current cannabis farmer Jim Belushi.
 

As the science and human cases demonstrate, cannabis shows immense potential for treating breast cancer. Patients deserve access to cannabis medicines now, and research is more than warranted to prove efficacy at the scale needed to make cannabis a formal anticancer treatment.