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 being 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".

He 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."

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 said: "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."