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Cannabis and cancer care: What the science says

health

Clearing the air

With legalization on the horizon in Canada, dispensaries are marketing marijuana as a cure for what ails you – including cancer. Do the claims hold up? Adriana Barton takes a closer look at the science behind cancer and cannabis

In a lab at the University of Nottingham in England, brain-cancer specialist Richard Grundy is growing cells from children's brain tumours to see if cannabidiol – a compound in marijuana – can kill them.

Brain-tumour cells rarely thrive outside the body, though, so he'll be lucky if half a dozen cell clusters survive long enough to study the hunch. Even if the compound snuffs out cancer cells in the lab, there's no guarantee it would do the same in humans. "But," he said, "one has to start somewhere."

That sums up the current stage of research on cannabis and cancer – it's at the start. Compelling stories of patient recoveries, combined with laboratory evidence of possible cancer-fighting effects, have spurred researchers worldwide to put cannabis to the test. So far, scientists have observed anti-tumour activity in cells cultured in Petri dishes or grafted onto mice. But mice and people are different beasts. Plenty of experimental cancer therapies have shown promise in early studies – such as dichloroacetic acid (DCA) – only to fail in human trials.

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But the cautious pace of medical research hasn't stopped Canada's unregulated marijuana dispensaries from marketing cannabis as a cancer cure. Some sell it with a veneer of science, quoting Harvard University researchers out of context as saying cannabis "significantly reduces the ability of the cancer to spread." Others link to a video with 1.2-million YouTube views featuring Rick Simpson, a Canadian living abroad who claims homegrown cannabis oil cured his skin cancer. Several websites take a conspiracy-theory approach, describing a high-potency cannabis oil called "Phoenix Tears" as "the cancer cure the government doesn't want you to know about."

As Canada hurtles toward new legislation to legalize marijuana in 2018, the buzz has left many Canadians wondering whether medical cannabis can help them recover from cancer. "It's a very common question we do get," said Robert Nuttall, assistant director of health policy at the Canadian Cancer Society, which outlines the facts about cannabis and cancer on its website.

No one can blame a cancer patient for wanting to try anything possible to get well – or at least take the edge off chemotherapy-induced nausea and other nasty side effects.

But when it comes to treatment, scientists have yet to determine whether marijuana's unproven anti-tumour properties outweighs the potential harms of consuming high-potency cannabis oils and extracts. To make sense of the evolving science, The Globe and Mail combed through the evidence and spoke to authorities in medical marijuana research. Here's our take on the burning questions about cannabis in cancer care.

What are cannabinoids? How can they help cancer patients?

Cannabinoids are the compounds in marijuana that have drug-like effects. THC, short for tetrahydrocannabinol, can dull pain and make people "high," while cannabidiol (CBD) may lower pain without psychoactive effects. These and other compounds in marijuana bind to receptors on cells throughout the body, including the brain, immune system and central nervous system, instructing cells to perform specific functions. In cancer patients, some of these instructions may help relieve chemotherapy side effects such as nausea, vomiting and appetite loss.

Do cancer patients have to smoke marijuana to get the benefits?

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No. In fact, inhaled cannabis has shown mixed results in studies of chemotherapy-induced nausea and vomiting. Instead, a doctor may prescribe an edible oil containing THC and CBD from a licensed medical cannabis producer, or a synthetic cannabinoid such as nabilone, an anti-nausea drug that mimics THC.

Before using cannabis in any form, Nuttall said, patients should discuss it with a medical doctor or oncologist to avoid side effects or possible drug interactions with their cancer treatments.

What are the upsides of medical cannabis for cancer symptoms?

Certain pharmaceutical drugs may be more effective in treating individual symptoms, such as chemotherapy-related nausea. But when doctors prescribe a different drug for each side effect, the pill count adds up, said Vincent Maida, a palliative medicine specialist at the University of Toronto and co-author of a 2016 guide to cannabinoid therapies in oncology published in the Canadian journal, Current Oncology. Since medical cannabis can relieve multiple symptoms, "we're able to help the pain, the nausea and the anorexia [appetite loss]."

Cannabinoids may also reduce dependence on opioid painkillers, said Maida, whose research is not funded by the medical cannabis industry (although he does accept occasional speaker's fees). Maida cites data showing that cancer patients on high-dose opioids are at greater risk for metastases (cancer spread), infections (opioids suppress the immune system) and opioid addiction. Expanding the use of cannabinoid therapies "can be regarded as an overall risk-reduction strategy."

What about a cure? Doesn't cannabis kill cancer cells?

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Certain chemicals derived from cannabis may kill tumour cells in a Petri dish, but so does bleach. That doesn't make bleach a cancer treatment. Testing compounds in Petri dishes, known as in vitro research, helps researchers gauge whether a substance shows enough effects to justify animal testing. But both in vitro and animal studies represent the earliest stages of medical research.

So far, the only published human trial of cannabinoids for tumours involved nine patients with terminal brain cancer. In this 2006 study, Spanish researchers injected medical-grade THC through a catheter in patients' brains, "which is different from people smoking a joint," Nuttall said. The researchers found signs of reduced tumour growth in cells taken from two patients, but all nine patients died from their tumours within months.

The authors emphasized they could draw no conclusions about THC's cancer-fighting potential based on the pilot study. There's a chance, in fact, that cannabis may have the opposite effect. In one in vitro study, published in 2010, researchers found that cannabinoids, under certain conditions, could interfere with the immune system's tumour-suppressing role. In a 2004 study and a 2005 study, cannabinoids appeared to stimulate cancer-cell growth.

It will take scientists years to figure how different types of cancer respond to specific compounds in marijuana, said Rukiyah Van Dross-Anderson, an associate professor of pharmacology and toxicology at East Carolina University. In 2016, she co-authored a review of dozens of studies looking at the effects of cannabinoids on cancers of the brain, digestive system, breast cancer, prostate, lungs, thyroid and skin. In a phone interview, she described the research as "promising," but added that so far "there is not enough evidence for any of the cancers to state confidently that it is effective and safe."

What about cancer patients who have gone into remission after using cannabis?

These are anecdotes, not evidence. In California, a cannabis company called Aunt Zelda's is building a database of reports from patients who say cannabis therapies helped them recover from cancer. But without rigorous medical documentation, no one knows whether the patient got better because of the cannabis, previous radiation and chemotherapy, or some other factor in the patient's life.

Rick Simpson of "marijuana miracle" fame may have bounced back from skin cancer, but a single remission hardly makes cannabis a one-size-fits-all treatment for the many different diseases we call cancer. Even the most promising findings suggest cannabinoids may shrink tumours, not eliminate them, Maida said. Hypothetically, if patients were suddenly free of cancer, "I would suspect that they were spontaneous remissions," he said. "And not an absolute cure induced by cannabinoids."

I have late-stage cancer. What have I got to lose?

For patients in end-of-life care, medical cannabis may reduce pain, help with sleep and improve mood. But as a "Hail Mary" treatment for terminal cancer, unregulated cannabis products can backfire. Marijuana dispensaries typically recommend extremely high doses of concentrated THC and/or CBD for cancer patients. These high-potency oils have no proven benefits over licensed medical marijuana – and may decrease quality of life, Maida said. At these levels, "you're going to make [patients] completely psychotic and sedated."

Do-it-yourself cancer therapy using products such as "Rick Simpson oil" or Phoenix Tears – sold as high-potency "cure-alls" through dozens of Canadian dispensaries – can easily cost more than $1,000 a month. But the biggest risk, particularly for patients with vulnerable immune systems, may be infection from bacterial or fungal contamination, or exposure to carcinogenic pesticides, Van Dross-Anderson said. Using a regulated product is the only way to ensure contaminants are removed. "I can understand people's desperation," she said, but instead of taking a chance on dispensary products, "it would be better to enroll in a clinical trial."

So what's the good news?

As marijuana loses it reefer-madness stigma, researchers are having an easier time securing funding and regulatory approval for research on cannabinoids, said Van Dross-Anderson, whose lab is studying the effects of a cannabinoid derivative on melanoma skin-cancer cells.

At the University of Canberra in Australia, researchers have gathered funding to conduct a human trial of cannabis therapy on patients with melanoma skin cancer, providing they produce safety data from animal trials and obtain ethical and regulatory approval. In Britain, GW Pharmaceuticals has completed a phase-two trial of cannabis compounds, combined with chemotherapy, in patients with glioma, an aggressive type of brain tumour. The company released initial findings in February, but the results have not been peer-reviewed or published in a medical journal.

Van Dross-Anderson speculates that cannabinoid treatments for glioma brain cancers – the most widely studied to date – may not be far off: "We could be looking at 10 years."

Grundy is more circumspect, but emphasizes the urgent need for more research. Parents of children with brain tumours often feel pressure from friends and family to give cannabis products a try, "even though there's no real evidence for it," he said. "I think it's a question that needs answers."

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