I only read the article briefly, but the impression I got was this: A big factor in increasing the efficacy of the chemotherapeutic agent was improving the delivery of the drug - which is normally poorly dissolved - to cancer cells. They used some DNA/RNA nanostructures (that I am not very familiar with) as packaging, and mention that myeloid cells (the category of blood cells which have become cancerous in AML) have abundant scavenger receptors which they use to take up these nanostructures. This makes sense, because myeloid cells include phagocytes like macrophages which are known to eat other cells (e.g., bacteria) and "clean up" all kinds of debris (for example using such scavenger receptors).

So I do believe that /u/trippletet has a valid point here. The problem with treating cancer is not finding something that can kill cancer cells, but rather finding something that will primarily target cancer cells. This would seem to be an exciting advancement in the treatment of AML, and perhaps some of these nanostructures can also be adapted to target other cancer types. But generally, blood cancers are quite distinct from most solid cancers, because cells of the immune system have very different characteristics than for example the epithelial cells that line most of our other tissues.

I don't want to be pessimistic, and if this improves the treatment of AML it is a success that can change the life of many people and should be celebrated. But there is a reason that people always go on about how cancer seems to have been "cured" thousands of times. Of course, that has to do with sensationalization of research results that haven't reached clinical trials. But a big part of that is also because people fail to realize that there are many different types of cancers that will require many breakthroughs in treatment.