Therapeutic advances in recent years have increased the chances of curing breast cancer. However, cancer drugs can cause severe side effects such as pain, nausea and anorexia (loss of appetite). This not only affects the quality of life. The success of the therapy is also at risk, as some people stop taking the cancer drugs because of severe side effects. Cannabinoids are on the rise to mitigate these side effects.
American researchers conducted an anonymous online survey of cannabis use among breast cancer patients in America. Respondents used cannabis to relieve various symptoms of cancer treatment: pain, insomnia, anxiety, stress, and nausea and vomiting. Cannabis products containing the psychotropic tetrahydrocannabinol (THC) as well as the non-intoxicating cannabidiol (CBD) were used most frequently.
Anonymous online survey among 612 breast cancer patients
A team of American researchers investigated cannabis use among American breast cancer patients in an online survey conducted between December 2019 and January 2020. The participants, who were on average 57 years old, were members of the health platforms breastcancer.org and healthline.com.
Among the 612 people who completed the survey, 605 were women and 5 were men. A further two people did not provide information on gender. A total of 42 percent (257 persons) stated that they used cannabis for medical purposes: 58 used cannabis exclusively for medical purposes and 199 also for recreational purposes.
The following was collected with open questions:
- Reasons for cannabis use
- Cannabis products used (medical or unregulated cannabis products)
- Perceptions on the safety of cannabinoids
- Sources for obtaining information on cannabis
Pain, sleep disorders and anxiety most frequently treated
Cannabinoids relieve distressing symptoms that can occur with cancer and chemotherapy or radiotherapy. In previous studies with cancer patients, pain, anxiety and nausea were the most common reasons for cannabis therapy.
Reasons for use of cannabis among breast cancer patients interviewed:
- 78 % Pain (acute and chronic nerve, joint or muscle pain)
- 70 % Insomnia
- 57 % Anxiety disorders
- 51 % Stress
- 46 % Nausea and vomiting
Tetrahydrocannabinol best researched
THC is the best-researched cannabinoid in medicine. The psychotropic effect can be accompanied by intoxication, mood elevation and sedation. According to current studies, THC alleviates pain (e.g. tumour and nerve pain), nausea and vomiting. THC-containing cannabis medicines include THC-dominant cannabis flowers and cannabis extracts, as well as medicines containing dronabinol or the synthetic THC derivative nabilone. Dronabinol and nabilone are approved in America for the treatment of chemotherapy-induced nausea and vomiting.
Further studies showed that insomnia and anxiety also decreased. THC improved sleep quality and recovery in patients with sleep apnoea, chronic non-tumour-related pain and multiple sclerosis.
Anxiety-relieving effects could also be observed in studies on chronic non-tumour pain, Tourette’s syndrome and multiple sclerosis. Further research is needed, however, as previous studies have focused on the underlying disease and effects on anxiety were only additionally recorded.
Cannabis in cancer therapy
Most (79 percent) of the interviewed cannabis patients used cannabis during cancer treatment. In addition to chemotherapy, breast cancer treatment can also consist of hormone therapies, immunotherapies, radiation and surgery. Almost half (49 percent) of the respondents also believed that cannabinoids have an anticarcinogenic effect, i.e., they can fight the tumour.
Animal studies are currently investigating whether cannabinoids can also stop tumour growth: Previous animal models for breast cancer showed that THC and CBD reduce tumour growth and metastasis, as scientists explained in a review paper published in 2020. However, clinical studies with affected individuals are still lacking. It is unclear whether the therapeutic successes can be transferred to humans. Future studies will further explore the potential of medicinal cannabis in breast cancer therapy.
CBD-dominant cannabis flowers and pure CBD preparations are most commonly used
The participants used a wide range of different cannabis products: Edibles (cannabis-containing food), liquid preparations (liquids, tinctures), smoked and vaporised cannabis flowers. Interviewed patients indicated different sources of supply such as state-regulated dispensaries, but also unregulated sources of supply such as the black market, friends or family.
Cannabis products are classified according to cannabinoid content:
- THC-dominant: medicinal and recreational cannabis contains mainly tetrahydrocannabinol in most cases.
- CBD-dominant: Commercial hemp, i.e. fibre hemp with THC concentrations below 0.3 percent mainly contains cannabidiol.
In the survey, most preferred CBD-dominant cannabis products or pure CBD preparations. Unlike THC, CBD is not psychotropic, but can also have a sedating effect in higher doses.
However, CBD-dominant cannabis products are less represented on both the medical cannabis market and the illicit market. For example, in a 2019 publication, only one-fifth of the 196 cannabis products offered at a medical dispensary contained CBD. Cannabis from the illicit market is mostly low in CBD. An American study showed that the THC content of illicit cannabis products increased in recent years: the THC content of cannabis flowers rose from 4 per cent in 1995 to 12 per cent in 2014. The CBD content, on the other hand, showed a reverse trend: the CBD concentration dropped from 0.28 percent in 2001 to 0.15 percent in 2014.
Interactions between medicinal cannabis and cytostatics as well as other medicinal products possible
However, taking medicinal cannabis with cytostatics and other drugs can also be risky: many drugs, including cannabinoids, are broken down via liver enzymes (CYP450 enzymes). Taking them at the same time as certain active substances can lead to interactions. Altered degradation of the medicines and cannabinoids can result in undesirable effects.
The enzyme CYP3A4 is involved in the metabolism of 60 percent of all drugs. THC and CBD inhibit this liver enzyme. In cancer therapy, in addition to cytostatics, numerous other active substances are used that also depend on CYP3A4: Antihistamines, azole antifungals, macrolide antibiotics and benzodiazepines. Since interactions have so far mainly been investigated in preclinical studies, the clinical significance is often still unclear. Studies with cancer patients are therefore necessary.
Lack of knowledge about medicinal cannabis
A large proportion (70 percent) of respondents perceived cannabis as a safe treatment, although many cannabis products are unregulated. Unregulated preparations may contain contaminants such as bacteria, fungi and pesticides.
Despite the high level of trust, there is a lack of good sources of information about medicinal cannabis. Half of the respondents (306 out of 612 people) informed themselves through different sources: Mostly the internet (22 percent), friends and family (18 percent) and non-pharmaceutical sales staff in cannabis dispensaries were the first point of contact. The fewest people affected sought medical advice: Only 12 people (4 percent) sought advice from doctors. The flood of dubious information on the internet is therefore particularly problematic.
Many medical professionals also feel inadequately trained regarding medical cannabis: A nationwide survey of 400 oncology physicians found that 70 % felt uncomfortable making treatment recommendations with medical cannabis. Almost a third (28 %) of the patients surveyed also felt uncomfortable bringing up the topic of medical cannabis during a doctor’s visit. This highlights the need for further research and education on cannabinoids for breast cancer.
Weiss, MC, Hibbs, JE, Buckley, ME, Danese, SR, Leitenberger, A, Bollmann-Jenkins, M, Meske, SW, Aliano-Ruiz, KE, McHugh, TW, Larson, SL, Le, EH, Green, NL, Gilman, PB, Kaklamani, VG, Chlebowski, RT, Martinez, DM. A Coala-T-Cannabis Survey Study of breast cancer patients’ use of cannabis before, during, and after treatment. Cancer. 2021. https://doi.org/10.1002/cncr.33906