Exosomes produced by cancer cells are very small, 100 nm in diameter, and they leak out into body fluids throughout the body.
Even in the very early stage of the disease, called precancerous state, cancer derived exosomes leak into urine, which is determined by the PCR investigation.
Tumor markers used in health checkups also detect cancer, however, they do not show abnormal values until the stage has advanced, so they do not detect cancer at an extremely early stage.