For decades, the central paradigm behind the treatment of most tumors has been “get it out”—or, if you can’t, kill it. But note that I said most tumors. For some, the best course isn’t necessarily one that focuses on killing the tumor, but one that also makes it grow up.

The cells of tumors like neuroblastoma or some kinds of acute leukemia aren’t necessarily wildly growing invaders full of murderous mutations. Rather, they’re immature. Instead of following the normal developmental path from stem cell to mature nerve (in the case of neuroblastoma) or white blood cell (in leukemia), something prevents the cells from maturing fully.

Mature or not, the cells can still grow without pause, quickly forming tumors or crowding healthy cells out.

The techniques for making cancer cells mature—or differentiate—differ greatly from those for making cancer cells die. But they hold promise for better, less toxic cures, especially for children with neuroblastoma, which next to brain tumors is the most common solid tumor of children. …