**2. The strategies for CTC isolation and enumeration**

There are hundreds of methods/protocols reported to be able to efficiently detect or isolate CTCs. In a simple way to discuss here, we have several common strategies of CTC isolation could be worthy of development in the future. The first one is **label‐free isolation strategy**, including size‐based, physical properties‐based, morphology‐based isolation strategy; the second one is **positive selection strategy**, including positively identification of cancer‐specific markers on nucleus or cell surface, or specific DNA mutation(s), mRNA(s) overexpression; and the third one is **negative selection strategy**, consisting of depletion of red and white blood cells by any means. Finally, the fourth one is combination of two or more strategies mentioned above.
