All of the livers above are from the same strain of mouse, which develops liver cancer. The livers on the right are from mice injected with virus that expresses a special microRNA that is usually lost in liver cancers. The livers on the left are from mice that were injected with a control virus. The animals were injected with the virus at the time when their livers had already developed small tumors, and then sacrificed for autopsy 8 weeks later. The same issue of Cell features another article about a microRNA that prevents breast cancer metastasis.
Despite their power, microRNAs are pretty new, and were discovered only through basic research:
The first microRNA was discovered in 1993, in worms. It took seven years for the second one to be found, also in worms, but then the floodgates burst.