No. It exists. In fact, that was the original intent of the technology.

About 15 years ago, I worked a summer job at an air traffic control center as a software analyst. At some point, there was a golf tournament organized as a fundraiser for cancer treatment research, followed by a supper. I did not attend the tournament that happened during the day, but I did attend the supper, which was right after my work day. Of course, some of the scientists were also in attendance. Normally, I would not have been invited to their table, but I had mentioned to one of them before we sat down that I'd survived cancer twice, so they were interested in speaking with me. I asked questions about their research, and they went in great detail about it.

Their method involved creating "viruses" that were specifically designed to target specific cancer cells. (It's possible that they only called them as such because they wanted to vulgarize their explanation for my benefit.) They would take a sample of the cancer cells in the specific patient, and then design the "virus" to specifically target and consume solely that one type of cell. When I asked about what was preventing the virus from mutating and targeting different parts of the body, their reply was that it was extremely unlikely, because the lifetime of the "virus" they injected was so short that they were more likely to die out as soon as their target was eliminated, before they were able to develop the ability to target different cells. They followed it up with specifying that they were still in the experimental phase, that it was not something doctors were allowed to recommend right off the bat as a possible cancer treatment, but that it was an option that was being floated around for patients for whom every other cancer treatment method failed. After all, not every part of the body can be targeted by radiotherapy, and chemotherapy only works for so long and to a certain extent. They mentioned a few cases where patients were only given a few months to live before their method was recommended to them, who were seemingly able to make full recoveries using it, and were still under observation for any side effects, which so far had not manifested in any way.

My impression after the discussion was that it sounded extremely promising, but limited. It was something that had to be customized for every patient, and for every cancer, which would clearly greatly increase the cost. It was not a method that could be used off-the-shelf, with a generic solution for everyone. It had to be very specifically tailored for the individual, else it wouldn't work and may target other cells, similarly to what chemotherapy does.

This method is absolutely not appropriate for creating vaccines. It seemingly could be called a "cure for cancer", but it is not universal or free, by any means. I fully support research and fundraising for mRNA treatments to cancer. I strongly oppose it for any intent it is not suited for.