Good question. I think this should answer your questions https://bmcmedgenomics.biomedcentral.com/articles/10.1186/s12920-020-0664-7 https://bmcmedgenomics.bio

Good question. I think this should answer your questions https://bmcmedgenomics.biomedcentral.com/articles/10.1186/s12920-020-0664-7 https://bmcmedgenomics.biomedcentral.com/articles/10.1186/s1... https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4009603/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4009603/ Speaking of detecting cancer indirectly, it is actually the fact that sometimes you can detect tumors (early) because their DNA or RNA products reach the blood or other bodily fluids (cfDNA/cfRNA for "circulating free"). It is a big and a recent thing - for many cancer types e.g. lung there was basically no easy way to test. Biopsies are very invasive obviously....