The difficulty in detecting a somatic mutation depends on its frequency within a cell population. Whereas mutations affecting a large fraction (e.g., 50%) of cells are readily detected in bulk tissue sequencing experiments and generally result in high-confidence calls, mutations affecting one or a few cells are unlikely to be detected with bulk tissue sequencing approaches. The identification and validation of rare somatic mutations requires sequencing DNA derived from small pools of cells, single cells, or clonally reprogrammed cells followed by robust computational data analyses (Fig. 1).
