From Dr. Hirst's Lab

http://www.nature.com/nature/journal/vaop/ncurrent/full/nature23666.html?WT.feed_name=subjects_developmental-biology&foxtrotcallback=true

Here they applied a technology developed in Dr. Hirst lab to track individual cells to study clonal evolution in human GBM.

Previous to this, clonal fitness has only been measured by genetic features - many of which may in fact be neutral.