From: Utility of circulating tumor DNA in cancer diagnostics with emphasis on early detection
Assumption | Justification | References |
---|---|---|
Fetal DNA in maternal circulation is proportionally related to fetal and maternal weight | It has been documented that, as maternal weight increases, the percent fetal DNA in maternal circulation proportionally decreases | [32] |
Circulating tumor DNA and circulating free DNA from normal tissues diffuse into the circulation at roughly equal rates and by similar mechanisms | ctDNA and cfDNA levels are quite variable between normal individuals and patients with cancer; however, as tumor volume increases, the amount of ctDNA also increases, correlating with tumor burden | |
In early cancer stages, the amount of ctDNA will not significantly affect the amount of total cfDNA or the circulating genome equivalents | In early stage cancer, the amount of ctDNA is only 0.1% or less, of total cfDNA; thus, it will not significantly increase the number of circulating genomes | |
Tumors are spherical and their weight and cellularity are proportional to the volume of the tumor; a tumor of 1Â cm3 has a wet weight of 1Â g and contains approximately 109 cells | Calculations are intended to be approximations in order to estimate the ratio of tumor/normal DNA in the circulation Abbosh et al. [21] reported that a 10Â cm3 tumor leads to 0.1% ctDNA in the circulation (see text for greater detail) |