Residual tumours were found to display higher percentages of DNA-PKcs immunopositive cells (Mean±s.e.m.: 67.8±5.5), compared with the corresponding primary tumour biopsy (Mean±s.e.m.: 57.8±5.2) (mean diff=9.95, s.d.=20.4, P=0.037). This evidence concerns the gene PRKDC and neoplasm.