From the article: "Once it had FDA approval, the team vaccinated six patients with advanced melanoma with a seven-shot course of patient-specific neoantigens vaccines. The breakthrough results were published in an 2017 article in Nature. For some patients, this treatment resulted in the immune system’s cells being activated and targeting the tumor cells.
The results, along with another paper published the same year led by the founders of mRNA vaccine company BioNTech, provided “proof of principle” that a vaccine can be targeted to a person’s specific tumor, Lendahl said." In a different article, "Cancer vaccine from BioNTech, Roche shows potential in small study," this was said:
“Although a very small study, this trial demonstrates the ability of mRNA vaccines to elicit potent anti-tumor T cell responses that appear to create significant clinical benefit,” said Ira Mellman, vice president of cancer immunology at Roche’s Genentech division and an author on the paper, in an emailed statement. “That such benefit was seen in pancreatic cancer, a lethal disease that has thus far been refractory to any form of immunotherapy, makes the result all the more exciting.”
Cancer is hard to treat because every cancer manifests the unique DNA of the specific patient and can vary from cell to cell. Even if you smash a tumor with potent drugs, it still tends to survive and grow again due to surviving tumor cells with advantageous genetic variations.
In concept, a vaccine properly targeted to an individual's unique DNA might activate the immune system to get at all the genetic variations of a tumor. This study suggests that might be true.