Thousands more patients with terminal cancer could go into remission if immunotherapy drugs were used in combination, scientists believe.
The drugs, which have boosted survival for dying patients, enable the body's immune system to hunt out and attack cancer cells.
But only around a fifth of patients get a good response to the therapies, and experts are looking for ways to drive up the number.
Clinical trials are starting to combine immunotherapy drugs instead of using them alone to increase their power. Adding immunotherapy to standard treatments is also producing positive results.
Addressing the American Society of Clinical Oncology (ASCO) conference in Chicago, US vice president Joe Biden, who lost his son Beau to brain cancer, spoke of the importance of the drugs, adding: "It wasn't that long ago that immunotherapy was out there somewhere in the hinterlands."
In one new trial - described as "one of the most exciting presentations" for ASCO by its chief medical officer, Richard Schilsky - patients with multiple myeloma experienced extraordinary results.
All 498 patients had cancer that had come back or had not responded to treatment. Half were given the immunotherapy drug Darzalax (daratumumab) in combination with two standard treatments, bortezomib and dexamethasone, while half received the standard treatments on their own.
The results showed that people given immunotherapy plus standard drugs had a 61% reduced risk of dying or their cancer getting worse than those given standard treatments.
Response rates also doubled with the addition of Darzalax. Some 59% of patients saw tumours shrink significantly, compared with 29% in the other group.
Nearly a fifth of patients (19%) had a complete response - which means doctors could find no trace of cancer in their bodies - compared with 9% given standard treatment.
Dr Antonio Palumbo, from the University of Torino in Italy, who led the study, described the results as "unprecedented" in myeloma, which is regarded as incurable and is extremely difficult to treat.
In other research, combining two immunotherapy drugs produced a response for almost half of patients with advanced lung cancer, which usually kills within a few months.
Some 38 patients were given two daily immunotherapy jabs, nivolumab and ipilimumab, and 47% responded, with more than 83% still alive after a year.
Professor Peter Johnson, Cancer Research UK's chief clinician, said the idea of combining immunotherapy drugs had the potential to benefit thousands of people in the UK.
He said more research was needed but added: "It's very exciting as it looks as though we can increase the power of the treatment.
"The darker side is that the side effects seem to be more common.
"It looks as though, if we can find new ways to combine different immune treatments, we'll be able to treat more patients effectively, and potentially to start using them in other types of cancer."
In another early-stage study presented at ASCO, a quarter of patients with advanced bladder cancer given immunotherapy as a first treatment instead of after other treatment also saw their tumours shrink.
Some 7% of the patients - who were all too frail or sick for chemotherapy - had a complete response and doctors could find no trace of cancer.
Dr Alan Worsley, senior science communication officer at Cancer Research UK, said many more patients could potentially achieve remission with combined therapies.
"Finding out which combinations of these drugs might work together is really exciting," he said. "How can we mix and match the number of options we have?"
He said last year's ASCO saw immunotherapy prove its "mettle" while trials are now looking at how it could be expanded to more cancers, combined with drugs and which patients would benefit the most.
Dr Worsley said some of the most important studies being presented at ASCO this year looked at immune checkpoint inhibitors - drugs that "try and take the breaks off the immune system".
The bladder cancer trial works on this principle and has produced a "a really dramatic effect" in a difficult to treat cancer, he said.