A cancer treatment that teaches the body to attack tumours will save the lives of tens of thousands of patients, researchers claim.

Experts believe it could be the biggest step forward since chemotherapy and could replace it within five years.

The treatment is particularly effective against some of the deadliest types of the disease including lung and skin cancer.

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Patients who underwent immunotherapy in a trial showed remarkable progress. Above, Vicky Brown's scans

Trials show that it has eradicated tumours in patients who were expected to survive for only a few months and they are now leading normal lives.

Called immunotherapy, it works by training the immune system to attack cancerous cells.

As well as lung and skin cancer, it has been hugely effective against kidney, bladder, and head and neck cancers, research from a number of key trials presented at the American Society for Clinical Oncology conference in Chicago shows.

These are some of the most aggressive types which are extremely difficult to treat and, together, claim the lives of 54,000 Britons every year.

In one British trial, patients with advanced skin cancer who would have been declared terminally ill are now back at work and are predicted to live until old age. Some may never need treatment again, others just require top-up sessions every few weeks or months.

Survivor: Vicky Brown said the treatment felt like 'a miracle drug'

One who has benefited from the new treatment is former college teacher Vicky Brown, 61, who was diagnosed with skin cancer in 2006 which returned and spread to her breasts and lungs. She was told in 2013 that she might live for only a few more months.

But she took part in the clinical trials at the Royal Marsden which began that August and within weeks the tumours had disappeared completely. Although it returned again, it was again eradicated by immunotherapy. It has come back a third time and doctors plan to use the same technique.

Mrs Brown, from Cardiff, said: ' It felt like a miracle drug. It has given me at least two years of life to enjoy – and hopefully many more. '

Professor Peter Johnson, director of medical oncology at Cancer Research UK, said: ' The evidence suggests we are at the beginning of a whole new era for cancer treatments. Not for every type of cancer, but for some of the ones we have struggled with the most.

'We are hoping that in many cases these effects will be maintained in the long term, possibly leading to cures for some.'

Professor Roy Herbst, chief of medical oncology at Yale Cancer Centre in the US, said that immunotherapy could replace chemotherapy as the 'standard treatment' for cancer within the next five years.

'I think we are seeing a paradigm shift in the way oncology is being treated,' he said. 'You can see a response as quickly as a couple of weeks. Some patients have amazing survival. '

Roger Perlmutter, president of research at the drugs firm Merck, which makes one of the main types of immunotherapy treatments, said: 'Immune manipulation may turn out to be an even more important intervention than chemotherapy was – maybe the most important ever.'

Although our immune system is trained to fight infections and cancer, some tumours are able to develop protective shields, meaning that the body's immune system, chemotherapy and other drugs are all ineffective.

Impact: During one trial in Britain 60 per cent of skin cancer cells, pictured under microscope, had either shrunk or been brought under control

But immunotherapy breaks down these shields and trains our body how to attack the tumours. Treatments are given in a drip every few weeks and typically cost around £100,000 per patient a year. Some types are already available on the NHS but others are awaiting approval by European regulators.

One trial, involving 950 British patients with advanced skin cancer, showed that for 60 per cent the tumours had either shrunk or been brought under control.

Dr James Larkin, a consultant at the Royal Marsden Hospital in London, who is overseeing it, said it was a 'game changer'. Although the trial began only two years ago, he said he hoped many would survive until old age.

More important than chemotherapy

'We have to be cautious about using the word cure but we've got patients who are basically free of melanoma (skin cancer) now, they're leading normal lives,' he said.

'By giving these drugs together you are effectively taking two brakes off the immune system rather than one so the immune system is able to recognise tumours it wasn't previously recognising and react to that and destroy them.

'For immunotherapies, we've never seen tumour shrinkage rates over 50% so that's very significant to see.

'This is a treatment modality that I think is going to have a big future for the treatment of cancer.'

The treatment does not work for all patients and some trials showed it was effective in only 25-50 per cent because it depends on the characteristics of their tumour.

But results from the skin cancer trial showed that combining two types of immunotherapy treatment benefited many more patients. So while one type was effective for 15 per cent of patients, two types combined worked for 60 per cent.

Experts hope that for all types of cancer, immunotherapy will be effective for at least half of patients.

The treatment is currently available for some NHS patients with skin cancer and the researchers argue its use should be widened for other cancers as soon as possible. The side-effects are less severe than for chemotherapy but include rashes, sickness and tiredness.

Experts hope that for all types of cancer, immunotherapy will be effective for at least half of patients (file image above shows chemotherapy)

Dr Alan Worsley, Cancer Research UK's senior science information officer, said: 'This research suggests that we could give a powerful one-two punch against advanced melanoma by combining immunotherapy treatments.

'Together these drugs could release the brakes on the immune system while blocking cancer's ability to hide from it.

'But combining these treatments also increases the likelihood of potentially quite severe side effects. Identifying which patients are most likely to benefit will be key to bringing our best weapons to bear against the disease.'