Q:I understand that cancer is caused by mutations in some of the genes that regulate cell growth and division. I also understand that patterns of which genes are likely to mutate, and how they will mutate, are reasonably well understood. Why then can we not use genetic engineering to make artificial viruses with RNA to fix the mutated genes and inject these viruses into tumors? Is there not enough space in a virus shell? If that is the case, then couldn’t we at least make viruses that could break the mutated genes completely?