From the time a baby is born, everyone receives a series of vaccines for chickenpox, hepatitis B, tuberculosis, polio, meningitis, and more. These once horrible diseases with extremely high mortality rates have been made less scary by the advent of vaccines. I, like many others, had a dream that every baby would be born with a “cancer vaccine” and that my family would never have to worry about it again. Vaccines are usually inactivated pathogens (viruses or bacteria). The vaccine does not cause disease, but looks almost exactly like the real pathogen, sort of like a model. This model is enough to cause an immune response, so small children often get fevers after vaccination. And crucially, the vaccine also triggers immune memory, so that when the real pathogen appears, the immune system quickly recognizes and clears it as if it had had the disease. What is a cancer vaccine? The key to developing an effective cancer vaccine lies in finding “cancer cell analogs” that resemble cancer cells in some ways, that elicit an immune response and immune memory, but that do not cause cancer. First of all, it is certain that there will not be a “broad spectrum cancer vaccine”, that is, there will not be a vaccine that can prevent all cancers. Because, as I said before, cancer is actually a collection of hundreds or even thousands of diseases, and each cancer is different, there cannot be one vaccine that can prevent all cancers, just as there cannot be one vaccine that can prevent all viral infections. Each cancer vaccine can necessarily target only a certain type of cancer or a certain genetic mutation. Depending on whether the vaccine is given before or after cancer, there are two types of cancer vaccines: “prophylactic vaccines” (which prevent cancer from occurring after vaccination) and “therapeutic vaccines” (which prevent further development and recurrence of cancer after it has occurred). Among the currently approved vaccines are preventive vaccines, namely the hepatitis B virus (HBV, which causes 80% of primary liver cancers) vaccine to prevent liver cancer and the human papilloma virus (HPV, which causes almost 100% of cervical cancers) vaccine. These two vaccines are very effective, but in fact they should be strictly considered virus vaccines, not cancer vaccines as we think, just because these two viruses are very closely related to cancer, so they were given the title of cancer vaccine, which is kind of a hype concept. The third vaccine, the first FDA-approved cancer vaccine in the true sense of the word: Provenge, a “therapeutic vaccine” for prostate cancer, was approved by the FDA, but its effectiveness was limited: the average survival time of patients after vaccination was only 4 months. With the emergence of two revolutionary new drugs for prostate cancer, Zytiga and Xtandi, the number of patients using Provenge has declined dramatically, and the company that manufactures it (Dendreon) has just recently declared bankruptcy. The company that made it (Dendreon) just recently announced its bankruptcy. It’s a shame that the company that had an endless halo back then is now out of business. In addition to the three approved vaccines, there are now more than 50 different cancer vaccines in clinical trials in the U.S. Similar to Provenge, they all use some kind of cancer cell analog (very complex, not much to say here) to elicit an immune response and immune memory.