The present disclosureprovides antibody polypeptides with binding specificity for prostate specific antigen (PSA), wherein the antibody polypeptide comprises: (a) a heavy chain variable region comprising the amino acid sequences TTGMGVS, HIYWDDKRYSTSLK and KGYYGYFDY and/or (b) a light chain variable region comprising the amino acid sequences and RASQNVNTDVA, STSYLQS and QQYSNYPLT, and wherein the heavy chain variable region and light chain variable region comprise framework amino acid sequences from one or more human antibodies. The application further provides use of said antibody polypeptides in the diagnosis and treatment of prostate cancer. The experimental results demonstrate that the humanised antibody h5A10, effectively targets prostate tumours in vivo, exhibits adly better tumor accumulation than its m5A10 and provides better imaging contrast (as shown with 15 higher tumor-to-organ ratios) than the murine antibody.
