Experts have hailed a "new era" for cancer treatment after developing a drug which can accelerate the immune system and "block cancer's ability to hide from it".
Immunotherapy, which harnesses the body's immune system to attack cancerous cells, is proving so effective that in one British-led trial, more than half of patients with advanced melanoma saw tumours shrink or brought under control.
The drug has a "big future for the treatment of cancer", researchers have said.
A number of trials of the drugs have been presented at the American Society of Clinical Oncology's annual conference in Chicago.
Professor Roy Herbst, chief of medical oncology at Yale Cancer Centre in the US, described some of the findings as "spectacular" and said immunotherapy could replace chemotherapy as the standard treatment for cancer within the next five years, according to reports.
He told reporters: "I think we are seeing a paradigm shift in the way oncology is being treated.
"The potential for long-term survival, effective cure, is definitely there."
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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."
An international trial on 945 patients with advanced melanoma saw them treated with the drugs ipilimumab and nivolumab.
The treatments stopped cancer advancing for nearly a year in 58% of cases, with tumours stable or shrinking for an average of 11.5 months, researchers found.
This was compared to 19% of cases for ipilimumab alone, with tumours stable or shrinking for an average of 2.5 months, according to the research published in the New England Journal of Medicine.
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Dr James Larkin, a consultant at the Royal Marsden Hospital and one of the UK's lead investigators, told the BBC: "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."
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."