In the last three years, at least £7m has been raised by people on crowdfunding sites like JustGiving and GoFundMe.

JustGiving's own figures show that more than 2,300 UK cancer-related appeals were set up on its site in 2016, a sevenfold rise on the number for 2015.

Many of the patients raising money have exhausted their treatment options on the NHS and are trying to fund expensive treatments elsewhere.

Some patients are seeking immunotherapy, a cutting-edge treatment, which has been shown to work in certain cases, but not all.

Others are seeking more dubious alternative treatments. Experts are concerned that desperate patients may be being given false hope and encouraged to spend money on unproven treatments.

Complementary or alternative?

Martin Ledwick, Cancer Research UK's head information nurse, said there was a difference between complementary medicines and treatments like yoga, acupuncture and massage, which might help improve wellbeing or quality of life, and alternative therapies which could replace conventional treatment.

"There isn't any proper scientific evidence that many alternative treatments work. Otherwise we would be using them. If people are spending lots of money on unproven treatments then that is very sad, as somebody is making money out of them," he said.

The crowdfunding figures were collected by the Good Thinking Society, a charity that promotes scientific thinking.

The society's project director, Michael Marshall, said: "Many proposals refer to specific drugs that have been discredited, extreme dietary regimes, intravenous vitamin C, alkaline therapy and other alternative treatments."

• Rise in crowdfunded cancer treatment
• Alternative cancer therapy survival risk
• 'I sold my house to fund cancer treatment in Germany'

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The popular alternative treatments that "don't work"

Gerson Therapy

The treatment: Gerson Therapy is a therapy established by a German doctor called Max Gerson in the 1920s and 1930s. It's based on a regimen of hourly raw and organic juices in addition to daily coffee enemas and heavy supplementation. Patients are often required to visit clinics in Mexico or Germany. Treatments can cost nearly £6,000 a week at these clinics.

The evidence: there is no scientific evidence that Gerson Therapy can treat cancer, and in some cases it could be harmful to your health.

The Alkaline Diet

The treatment: this is based on the idea that cancer thrives in an acidic environment, and that by changing the body's PH level to be more alkaline will make the environment unwelcoming to cancer. The diet suggests eating more "alkaline" foods like green vegetables and fruit.

The Evidence: Blood is usually slightly alkaline. It can't be changed for any meaningful amount of time by what you eat, and any extra acid or alkali is simply passed out in urine. There is no evidence to show that diet can manipulate whole body PH, or that is has an impact on cancer.

Antineoplaston

The treatment: Invented by Dr Stanislaw Burzynski, and promoted by his clinic in Houston, the therapy is based on the idea that peptides isolated from urine can be used to cure cancer. Patients enter into "clinical trials" at large cost to themselves.

The evidence: The only clinic reporting positive results for trials is Dr Burzynski's own clinic. No other researchers have been able to show that this type of treatment helps to treat cancer.

High-dose vitamin C

The treatment: High doses of vitamin C are intravenously fed into the bloodstream. A number of clinical trials, mainly in the US, are researching this.

The evidence: So far no reliable evidence that intravenous high-dose vitamin C helps treat cancer. It also may interfere with how radiotherapy works.

Source: Cancer Research UK

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Treatments at early stage testing

Cannabis Oil/CBD

While there is some evidence that cannabinoids might slow tumour growth in the laboratory, there is no sufficient evidence in patients yet to support this.

Many trials are ongoing. Cannabis is still classified as a class B drug in the UK, and as such it is illegal to possess or supply it. Cancer Research UK offers a detailed analysis of the the current research.

Hyperthermia

Hyperthermia (also called thermal therapy or thermotherapy) is a type of cancer treatment in which body tissue is exposed to high temperatures. Research has shown that high temperatures can damage and kill cancer cells, usually with minimal injury to normal tissues. Yet studies are still at an early stage, and it is not widely available.

The National Cancer Institute USA has more information on clinical trials.

Source: BBCNews Health