For Eileen O’Sullivan, being diagnosed with breast cancer in 2013 was the catalyst for a deluge of distinctly unscientific and frequently dangerous advice. An investment manager with a analytical mind, she began seeking information to better understand her potentially life-altering condition. But from the moment Eileen starting searching online, misinformation was unavoidable: “This is when all the suggestions start rolling in,” she says. “Before diagnosis, I had never heard of crank treatments for cancer: herbs, supplements, diets, juicing, clean eating, homeopathy, essential oils, nor adverts for overseas alternative cancer clinics. I certainly didn’t go looking for them, but I got endless prompts based on keywords such as breast cancer. I was also inundated with relatives and friends coming out with crackpot therapies – and even from other patients in chemo wards and waiting rooms.”

As a cancer researcher deeply involved in science outreach, I can attest that few subjects provoke quite the emotional response that cancer does. There is not a family in the world untouched by the disease, and the word itself is enough to induce a sense of fear in even the hardiest among us. Cancer is oppressive and all-pervasive: half of us alive today will experience a direct brush with it. But despite its ubiquity, it remains poorly understood and falsehoods around it can thrive.

Online, dubious claims about cancer are rife, from outright “cures” to assertions of a conspiracy to suppress “the truth” about it. In 2016, more than half of the 20 most shared cancer articles on Facebook consisted of medically discredited claims. And this goes far beyond Facebook – the Wall Street Journal recently revealed that YouTube was hosting accounts with thousands of subscribers that promoted bogus cancer treatments. O’Sullivan’s scepticism gave her some immunity to the lure of empty promises. But having lost her mother to breast cancer, “fear left me more vulnerable to pseudoscience than I would care to admit”, she says.

She is now a passionate patient advocate, steering others away from damaging falsehoods – a problem she sees as unrelenting. This grim assessment chimes with the observations made by Dr Robert O’Connor of the Irish Cancer Society: “Practically all patients are exposed to misinformation, [coming] from well-meaning but misinformed loved ones to a plethora of exploitative and profiteering sources on social media”.

A quick web search reveals ostensible treatments ranging from the vaguely scientific-sounding to the profoundly esoteric. The US Food and Drug Administration’s (FDA) non-exhaustive list of debunked claims numbers more than 187, while Wikipedia’s list of bogus cures run from “energy-based” to “spiritual healing”. Other claims involve hyperbaric oxygen therapy, cannabis oil, shark cartilage, ketogenic diets and baking soda.

There is increasing concern that such fictions risk eclipsing reputable information. Macmillan Cancer Support recently appointed a nurse specifically to debunk online stories, prompting the Lancet Oncology to comment: “How has society got to this point, where unproven interventions are being chosen in preference to evidence-based, effective treatments? Unfortunately, disinformation and – frankly – lies are widely propagated and with the same magnitude as verified evidence.”

Radiotherapy and chemotherapy are dismissed by charlatans as poisons, imperilling lives

Similar concerns are echoed by Cancer Research UK as well as the Wellcome Trust. New patients in particular are often targeted by those pushing cancer “cures”, and while some of these are well meaning but misguided, others are commercially driven. Sonya Canavan, another cancer survivor, noted: “In the breast cancer patient forum I used to post on, I often saw ‘patients’ posting about all kinds of quackery, who turned out to be salespeople trawling for business.”

That pseudoscience is being hawked to vulnerable patients isn’t a new problem – cancer scams have existed for decades, and combating them was the impetus behind the 1939 Cancer Act. The substantial difference now is the ease with which falsehoods can be disseminated. Cancer surgeon David Gorski, professor of surgery and oncology at the Wayne State University School of Medicine in Detroit, Michigan and managing editor of the online journal Science-Based Medicine, notes that cancer misinformation is “way more prevalent now for the same reason other misinformation and conspiracy theories are so prevalent – because they’re so easily spread on social media.”

Whether born out of a desire to help, or naked charlatanism, the net impact of such misinformation is overwhelmingly negative. Patients engaged with unproved treatments for cancer are more likely to reject conventional treatment, or delay life-saving interventions. This comes at a terrible cost; patients who subscribe to alternative approaches are more than twice as likely to die in the same period as those who rely on conventional therapies. Worse again, it is not uncommon for promoters of dubious information to resort to scaremongering over conventional therapy. Both radiotherapy and chemotherapy are frequently dismissed as “poisons”, imperilling lives. Cancer is frightening, and promises of simple cures can be alluring.

Facebook Twitter Pinterest Stanislaw Burzynski in 1997 at the federal courthouse in Houston, Texas, where he faced 34 charges of mail fraud, which were dismissed, and 41 of violating FDA regulations, upon which the jury failed to reach a verdict. Photograph: Pat Sullivan/AP

All false claims betray the same basic misunderstanding, however: cancer is not a monolithic entity, but a family of more than 200 known diseases. Arising from mutations in a patient’s cells, cancer is extremely complex and diverse. It is highly unlikely that a single “magic bullet” could treat cancer in all its forms. The idea of a panacea is attractive, but woefully misguided, and a klaxon warning of dubious science. Unscientific interventions can nevertheless come with substantial price tags.

Based in his Texas clinic, Stanislaw Burzynski claims to cure cancer with a unique “antineoplaston” therapy. Despite operating for decades, according to the US National Cancer Institute (NCI) “other investigators have been unable to duplicate these results”. Since its inception, the clinic has been the subject of numerous FDA warnings yet continues to promote itself as capable of curing patients. And it does not come cheap – the US NCI warns patients that treatment costs upwards of $7,500-$10,000 monthly (£5,600-£7,580) and says: “The evidence for use of antineoplaston therapy as a treatment for cancer is inconclusive. Controlled clinical trials are necessary to assess the value of this therapy.”

Despite negative publicity, it’s business as usual for Burzynski. If anything, crowdfunding may have made his clinic more popular. In lieu of scientific evidence, it relies on gushing testimonials to lure new customers, though in some cases, these come from patients already deceased – a fact absent from the promotional material.

This is contemptible, but in no way unique – there is an abundance of dubious clinics worldwide promising the impossible at eye-watering prices. Last year an investigation on Irish television probed clinics in Istanbul that were claiming huge successes with unconventional therapies. Patients were charged more than €130,000 (£116,000) and given the all-clear in Turkey. According to the programme, patients discovered their cancers had progressed markedly when scanned after returning home. Germany, too, is home to several effectively unregulated clinics, presented as luxury spas but promising cures. These are backed by fawning testimonials pitched at international customers, with treatments costing hundreds of thousands of euros – despite no evidence for their efficacy.

Such exploitation goes far beyond the immediate victims, with crowdfunding typically used to meet their exorbitant prices. A paper in the British Medical Journal last year, based on figures collected by the Good Thinking Society, found that at least £8m had been raised since 2012 in the UK alone for unsubstantiated or discredited cancer treatments. As Good Thinking Society project director Michael Marshall explains: “Sums raised through crowdfunding are just the tip of the iceberg, with many patients taking out loans, mortgaging their houses, and spending their life savings. When these supposed cures turn out to offer no benefit, families have been left coping with huge debts when they are grieving for their loved one.”

To explain the paucity of evidence for their claims, purveyors of quack remedies accuse the medical and scientific community of suppressing cures for cancer. This is not a mere fringe belief – 37% of Americans believe the FDA is doing just that. But the claim is nonsense. It would require a vast conspiracy of hundreds of thousands of scientists and doctors to sustain – a scenario unlikely to endure.

Plus, if there were such a conspiracy, wouldn’t those who work in the cancer sphere be just as susceptible to its malignant influence as anyone? We all lose loved ones to cancer, and succumb to it. Conspiracy claims foster distrust between patients and healthcare teams.

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The rise in cancer misinformation is part of a wider problem with online falsehoods. Like the equally dangerous explosion in anti-vaccine myths, cancer untruths have an impact on both our physical wellbeing and on the public understanding of science and medicine. In a sea of sound and fury, discerning between the reputable and the repugnant isn’t always easy, but there are excellent resources available for patients and their families. Well-researched guides by Cancer Research UK and the US National Cancer Institute are enlightening and authoritative.

Like anti-vaccine sentiment, cancer myths thrive on social media. There is a strong argument that these platforms have a moral obligation to remove groups and individuals propagating misinformation. As O’Sullivan notes, “Facebook, YouTube and Twitter lead a patient down a rabbit hole, with many thinking this is ‘doing their research’. I don’t think we can stop those making false cancer claims, but maybe we can insulate patients and regulate those making cancer claims as well as holding social media platforms accountable.”

In the wake of a measles resurgence driven in part by online anti-vaccine activism, several social media platforms have promised to massage their algorithms to reduce “fake news” on cancer. But this filtering is easily bypassed. Social media business models thrive on engagement rather than veracity, and a cynic might think they have little reason to regulate such content, beyond appearing to be concerned. Whether the problem is absence of ability or inclination, health misinformation remains widespread. It’s imperative we improve our ability to assess the avalanche of medical claims: our continued wellbeing depends on it.

Dr David Robert Grimes is a cancer researcher, physicist and science writer. His first book, The Irrational Ape: Why Flawed Logic Puts Us All at Risk, and How Critical Thinking Can Save the World, will be published by Simon & Schuster in September