It is a big black box. A prospective study is impossible to do. There are 71 licensed vaccines for cats in the United States. Retrospective studies have been hampered by incomplete records of manufacturers, lot numbers, and vaccination sites. It is important to get as many cases together for trials as possible, and the vaccination protocol is the best way to do so.
All species can get trauma-associated malignancies, but cats are particularly susceptible.
A wound that takes a long time to heal or any chronic irritation will induce a large number of cell replications, producing new cells necessary for healing. The more cell replications, the more likely the chance of an error or mutation that becomes a cancer. Cats have developed sarcomas at sites of antibiotic and even steroid injections. The consensus from the veterinarian community is that cats should be vaccinated in accordance with the manufacturers' recommendations and the vaccination protocol. Monitor your cat's vaccination sites for lumps.