Comment by odyssey7

I get that radiation is generally biocidal, but so are a lot of things.

Following the reasoning of the parent comment,

> It's seems to me, as a layman, that the hard part would be designing the "targeting" end of the drug

It fits nicely with this statement:

> An individual tumor often comprises of many subclonal cancer cell populations, all of which could have unique resistance mechanisms

If the unique features of a tumor cell are the lock, then your search space has a relatively small number of keys, compared to a larger toolkit of known biocides. The key needs to fit a specific cancer cell, while the biocide merely needs to avoid the cancer cell’s needle-in-a-haystack resistance mechanisms, which are tailored for surviving in the human body rather than against laboratory chemicals. The harder problem seems to be finding the one or more keys needed to target a diverse population of cancer cells.