Skip to main content
Figure 1 | Genome Medicine

Figure 1

From: Circulating tumor cells and DNA as liquid biopsies

Figure 1

Monitoring of tumor genomes using CTCs and ctDNA. Cancer cells can disseminate from the primary site through the lymphatic system (not shown) or by hematogenous routes. In addition, tumor cells can release DNA into the circulation (illustrated as small DNA strands). The figure shows a tumor consisting of two clones, center, indicated in dark and light blue. In this example the light blue clone releases CTCs and DNA into the circulation at a given time. Analysis of CTCs and ctDNA can reveal tumor-specific copy number changes (chromosome 8 is included here as an example, and is depicted as an overrepresentation of the long arm) and mutations at the nucleotide level (illustrated as the allele fraction of mutations at the bottom). If the tumor genome is stable, repeated analyses would reveal no additional copy number changes or mutations. However, cells from one clone may decrease (left, the light blue clone) as a result of selection pressures associated with a given treatment, whereas cells from another (dark blue clone) increase so that CTCs and ctDNA from this clone may be preferentially released into the circulation. As the material in the circulation is now from a different clone, copy number changes (here illustrated as a loss of the entire chromosome 8) and the allele frequency of mutations may differ substantially from the previous analysis. Alternatively (right), the light blue clone could acquire a new mutation - for example, with increased resistance to a given therapy (shown as green cells) - and because they evolved directly from the light blue cells, copy numbers and mutations will be very similar to the earlier analysis. However, new mutations may be detected (indicated here as a high level amplification on 8q and a new mutation).

Back to article page