Nature looks at the chaotic state of bringing cancer vaccines to trial: "Many first-generation cancer vaccines such as PANVAC, a pancreatic cancer vaccine, were deemed safe but failed to demonstrate that they significantly slowed the progression of cancer. Because cancer-associated antigens - such as those used in Provenge - are also found at low levels in healthy tissue, their ability to trigger a powerful immune response may be blunted. A second generation of vaccines, designed to provoke a stronger immune response, is under development, with some scientists now focusing on antigens that are found only on tumour cells. ... Over the past decade, researchers have reached a deeper understanding of how tumours actively suppress immune responses in their immediate environment, which can dampen responses to cancer vaccines. To overcome this, some therapies currently in development combine the vaccine with chemotherapies that are designed to counteract this immune suppression. ... For some in the field, the struggle to create effective cancer vaccines conjures up memories of the long battle to develop antibody-based therapies, which are now a mainstay of the biotechnology industry. There, too, a series of clinical-trial failures initially soured the field's reputation ... We realized you just have to test a lot of drugs to find one that works, and it's the same for a cancer vaccine."