TKT and neoplasm: For example, normal gene insertion into tumor cells to replace a mutant gene (e.g., p53), infection with oncolytic viruses to selectively replicate and lyse tumor cells (e.g., replication‐deficient adenovirus), and the tumor‐specific expression of suicide genes which convert inactive pro‐drugs into active drugs (e.g., herpes virus thymidine kinase [HSV‐tk] combined with ganciclovir [GCV]).2