Sure--you won't be able to get every tumor. But there are certain markers that are more common than others, so if you can get the top ~10 done within reasonable

Sure--you won't be able to get every tumor. But there are certain markers that are more common than others, so if you can get the top ~10 done within reasonable measures of safety, you could prevent a nontrivial number of cancers. There are a handful of embryonic proteins that are normally expressed during development but are absent in the adult that are particularly promising. One of the hallmarks of cancer is dedifferentiation--losing specific markers and function and looking more and more like a stem cell that can continue to replicate, and these embryonic proteins are known to be reexpressed in many tumors.