Method: To improve the reliability of the assay for tumour cell detection modifications were incorporated into the protocol. These include repeating the molecular test from new tissue sections when a single tumour-positive plaque is identified. We also recommend reamplifying (stabbing) rare positive plaques to confirm that they represent residual cancer. Difficulties inherent in examining gene deletions and designing oligonucleotide probes, which consistently distinguish mutant from wild-type p53 gene mutations, will be described.
Results: Interim analysis of the cases enrolled in the clinical trial reveals that many patients with p53 mutation positive residual cancer develop a recurrence, despite receiving postoperative radiotherapy. This strongly suggests that these cases have radioresistant residual disease.
Conclusions: However, locoregional recurrence also develops in cases with tumours that do not harbour p53 gene mutations, highlighting the need to develop alternative strategies for tumour cell detection for these cases. As the phage plaque assay is extremely cumbersome and time consuming and frequently needs to be repeated, a new rapid approach is required to facilitate incorporation of molecular diagnostics into treatment trials.