Several ELISA kits exploiting a sandwich assay construction exist on the market, for research purposes only, whose sensitivity and selectivity may be insufficient for precise determination of HER-2/neu at clinically requested, from 10−11 to 10−10 M HER-2/neu, serum levels (with a cancer cut-off at 2 × 10−10 M) [102]. Here, ERBB2 is linked to cancer.