The rate at which these tumors occur is quite small, and should not keep you from vaccinating your cat. What you should do is watch the vaccination site for any lumps or bumps. Lumps are common after a vaccination within 2-3 weeks. These vaccine reactions should get smaller and harder and finally disappear with time. If you cat has a lump that is persisting or getting larger see your veterinarian.
Vaccination is probably one of the main reasons that pets are living healthier longer lives.
Make sure you tell your vet who will then tell the vaccine company about any reactions that occur. So I cannot provide diagnoses, or really tell you to ignore or treat a given problem. I hope the information provided guides you in making good health care decisions for your pets.