There also are agents being used in medicine on other diseases that are accidentally found to protect against cancer.
Metformin is a diabetes drug, been around for years. Clinics noticed that diabetics on Metformin got cancer at a lower rate than the general population. Now Metformin is prescribed sometimes as a cancer fighter. Today there are many agents that can be used against cancer, and they can be combined to enhance effect. Pharmacological approaches can be more effective that surgery and radiation.
Metformin is also a fertility drug for women with PCOS.