Experts have hailed a "new era" for cancer treatments after achieving "spectacular" results from trials on a new class of drugs.
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, researchers 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."
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 t umours 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.
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."
Eminent oncologist Professor Karol Sikora, the dean of the University of Buckingham's medical school, cautioned against expectations of "miraculous breakthroughs" from the latest discoveries.
Prof Sikora told the BBC Radio 4 Today programme: "The immune system has been known to affect certain cancers when stimulated for the last 100 years, but we haven't quite got round it yet.
"The current discoveries being released in Chicago, the media pick them up and for cancer patients it's very sad. You would think cancer was being cured tomorrow. It's not the case. We've got a lot to learn.
"The prolongation of survival from these very expensive immune therapies is often a matter of weeks or months and we've got to make it long-lasting and that has to be our priority.
"I'm afraid it's mixed news. There are breakthroughs coming, there is hope for cancer, that we will do much better in the future.
"It's slow progress, rather than miraculous breakthroughs, as it's likely to be reported."