Objective To obtain antibodies against CA50 antigen with high affinity and specificity,and to establish a diagnostic kit so as to enhance the specificity and sensitivity of the diagnosis of tumor related diseases. Methods The mouse single chain antibody( ScFv) genes were obtained by PCR and cloned into pcomb3 XSS phagemids. ScFv phage antibody library was obtained by electrotransformation. CA50 antigen containing epitope LST a( sialic acid lactose-N-four sugar a) was used for the elutriation screening. Rand...