that greater than 15-20% of cells contain the mutation for most sequencing methods. The selection of pure tumor cells prior to sample processing can further exaggerate apparent variations in analytic sensitivity, so that a study utilizing relatively insensitive conventional sequencing, along with selection for tumor cells, will likely vastly underestimate
https://www.amp.org/AMP/assets/File/position-statements/2010/AMPAHRQCommentlette...