Cancer is a generic name used to classify a large group of diseases that manifest themselves due to the uncontrolled growth of abnormal cells. Healthy cells in an organism are constantly developing, dividing and dying. Cancer is diagnosed when cells in one part of the body begin to grow out of control. Most of the time, cancer cells form a tumor and continue to grow, instead of dying, and can even invade other healthy tissues through the bloodstream and lymphatic vessels, a process called metastasis. According to the National Cancer Institute, each year, around 600,000 new cases are diagnosed in Brazil. When left untreated, cancers can lead to more serious illness and death.

Cancer is considered a genetic disease because it is caused by changes in genes that control the way cells function. Although these changes are hereditary, they can also manifest themselves throughout a person’s life. There are more than 100 types of cancer, commonly named by the organ or tissue affected.

Treatment of the disease depends on the location and how advanced it is. However, there are a number of treatments which include: surgery (which involves removing the cancerous tumour); radiation therapy (uses high doses of radiation to kill diseased cells and shrink tumors); chemotherapy (uses drugs to kill affected cells); immunotherapy (which helps the immune system fight cancer); hormonal therapy (slows or stops the growth of cancer that develops on the basis of hormones); targeted therapy (targets changes in cancer cells that help them grow and divide) and stem cell transplantation, involving a procedure that restores blood-forming stem cells in people who have had theirs destroyed by other cancer treatments.

Discoveries: effects of cannabis on cancer

Evidence suggests that cannabis has the potential to inhibit the growth and even kill cancer cells, while helping patients manage symptoms associated with cancer treatments. After evaluating the available literature, a recent review of research concluded that cannabis has antitumor properties and is effective in relieving pain, nausea, and vomiting in cancer patients 107.

Two of the main cannabinoids found in cannabis, THC (tetrahydrocannabinol) and CBD (cannabidiol), activate the CB1 and CB2 cannabinoid receptors of the endocannabinoid system. Activation of these receptors by cannabinoids can trigger antitumor effects in a number of aggressive cancers. THC and CBD have been shown to inhibit the progression of breast, lung, prostate, and intestinal cancers in animal models, suggesting that cannabinoids may also be effective in mediating cancer cell death in humans 35,53,63,74.

In another study with humans, CBDa – CBD in its acidic form – demonstrated the ability to deregulate breast cancer cells, preventing their growth 93. In 2016, the same team of researchers discovered that CBDa is capable of inhibiting the migration of breast cancer cells by identifying that this effect was associated with the deregulation of the c-Fos proto-oncogene and the cyclooxygenase-2 enzyme 94. Cannabis has long been demonstrated to be able to offer relief to patients suffering from nausea related to cancer treatments. Studies have found that CBD is effective in treating more difficult-to-control symptoms such as nausea, as well as preventing anticipatory nausea related to chemotherapy patients 56,76. Another study found THC to be effective in reducing conditioned rejection and chemotherapy-induced nausea 54.

Cannabis has also been shown to be effective in reducing neuropathic pain that traditional treatments cannot manage 108. In one study, cancer patients with difficult-to-control pain who had tried unsuccessfully to manage their discomfort with opioids achieved significant reductions in pain levels after being treated with cannabis containing both THC and CBD for two weeks 47.

Weight and appetite loss caused by nausea are common side effects of cancer treatment. However, THC has been shown to significantly stimulate the appetite of patients who experience cachexia, a complex and multifactorial syndrome characterized by loss of weight and appetite, muscle atrophy, fatigue and weakness 46,70. Patients treated with THC have a better appetite and report that food “tastes better” 10. The ability to stimulate the appetite of cancer patients is significant in helping to prevent cachexia associated with cancer treatments.

Research that analyzed the effects of cannabis on 131 cancer patients after 6-8 weeks of treatment showed significant improvements in all measurable symptoms associated with the disease, such as nausea, vomiting, mood disorder, anorexia, constipation, sexual dysfunction, sleep disturbances, itching and pain 3. Patients treated with THC also experience improved sleep and relaxation 10. The National Cancer Institute, an organization administered by the United States Department of Health and Human Services, recognizes cannabis as an effective treatment in relieving a range of symptoms associated with cancer, including pain, nausea and vomiting, anxiety and loss of appetite 15.

Recent studies on the effects of cannabis on cancer

• CBDA inhibits the migration of breast cancer cells. Selected cannabidiolic acid-mediated c-Fos dysregulation in MDA-MB-231 cells from aggressive breast cancers: possible involvement of its dysregulation in the abrogation of aggressiveness. http://link.springer.com/article/10.1007%2Fs11418-016-1030-0
• Research review concludes that cannabis has antitumor effects and is effective in reducing chemotherapy-induced pain, nausea, and vomiting. Use of medical marijuana in oncology: a review http://jamanetwork.com/journals/jamaoncology/fullarticle/2504173
• Animal studies have shown that cannabis-derived CBD inhibits the progression of many types of cancer (glioblastoma, breast, lung, prostate, intestine). The antitumor activity of plant-derived non-psychoactive cannabinoids.
  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4470774/
• Cannabis causes significant improvement in nausea, vomiting, mood disorders, fatigue, weight loss, anorexia, constipation, sexual function, sleep disturbances, itching and pain in cancer patients after 6-8 weeks of use. The medical need for medicinal cannabis: prospective observational study evaluating the treatment of cancer patients in palliative and supportive care.
  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3730175/

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