Keywords Biomarker: A detectable cell characteristic that tells us something about its biological state. CTC: Circulating tumor cell. Read about what they are and why they’re important here. I have been out of town most of this week at the World CTC Conference in Boston, which was a great forum to hear about the latest in CTC research, and I had a very engaged audience at my presentation. However, I didn’t have time to write up my next post in my series on sorting techniques.