ST8SIA4 and cancer: Unfortunately, the intracellular antigens reactive with anti-dPSA antibodies, which are prevalent in both normal and cancer cells [21] remain unidentified but appear to be unrelated to membrane-associated dPSA based on immune-dot blots of subcellular fractions from CHP-134 ST8SIA2 and ST8SIA2 + ST8SIA4 double knockout cell lines (Additional file 2, Supplementary Fig. S6).