I don't know if chronic opioid exposure drives other cells to death. It certainly does cause some neuronal death, which we've already established with other opioids, also using the ATF4 mechanism. The tumor in this paper is a brain tumor.

AKA, drug belonging to [drug class] that kills [neuronal tissue] will also kill [bad neuronal tissue] through same mechanism as [general drug class].

The key question is "if putting a shit-ton of opioids (which already cross into the brain) in cancer patients doesn't already meaningfully treat this condition, why do we imagine that delivering the same class of drug past the blood-brain barrier suddenly will?"

Having worked in a breast cancer lab once upon a time, I can tell you: because run-of-the-mill cell biology doesn't get grant funding if you don't attach "early cancer diagnostics" or "potential cancer treatment" to the grant application.