An STD gives one the cancer
More correctly, this STD left untreated, can (not always) cancer. If these girls were checked regularly, it could be discovered and treated before it develops into cancer, which takes years of untreated infection to do.
Meanwhile, the little disease carrier is a host, spreading the disease by either being used as a sperm depoitory, or sharing her dildo with her friends; after all, they teach "sex is fun and gay sex is fun too" in schools now.