Regardless of which biological fluid is chosen, the aim is to evaluate the presence of circulating tumor cells (CTCs), circulating extracellular nucleic acids, such as those found in circulating tumor DNA (ctDNA), microRNA (miRNA), extracellular vesicles, nucleosomes, and various glycoproteins and antigens, such as CA-125, CA-19-9, CEA, and many others [46]. This evidence concerns the gene CEACAM5 and neoplasm.