Since the shedding of the ErbB2 extracellular domain by malignant cells into the bloodstream is commonly observed in patients harboring ErbB2-positive cancers, circulating ErbB2 has been previously proposed as a novel circulating biomarker and, curiously, had its performance found comparable to the one of CA 19.9 [52,53,54]. Here, ERBB2 is linked to cancer.