Many proteins were found to bind onto HG4 (Fig. 3A and Figure S3A) with LC–MS/MS analysis revealing that HG- and HG5 bound alpha-2-HS-glycoprotein and albumin, both proteins abundantly present in serum, whereas several types of serum-derived factors, reported to have cancer-promoting functions, were identified on the hit gel PA531-HG4-binding proteins (Fig. 3B). Here, PKD1P4 is linked to cancer.