The Ligamp TP53 Assay for Detection of Minimal Residual Disease in Head and Neck Squamous Cell Carcinoma Surgical Margins

Purpose: Detect tumor-related DNA using LigAmp in histologically clear margins and associate results with clinical outcome. Experimental Design: Patients with head and neck cancer were registered for molecular analysis of surgical margins. Adequacy of resection was ensured using histologic margin analysis. Further margins were then harvested and DNA extracted. TP53 mutations in tumor were determined using Affymetrix p53 GeneChip. Margins were analyzed by Ligamp in comparison with standard curves for quantification of mutant DNA. Ligation used two oligonucleotides to isolate DNA targeting the mutation. Ligated DNA was amplified using real-time PCR. The quantity of mutation in the margin was determined as percent of mutant species relative to plasmid and relative to tumor. Cutpoints were identified and defined groups were evaluated for local failure-free, cancer-specific, and overall survival. Study margins were examined for presence of tumor by light microscopy. Results: Tissue from 95 patients with common mutations was analyzed. Fifteen experienced local recurrence. Cutpoints of 0.15% for mutant species relative to plasmid and 0.5% for mutant species relative to tumor were chosen as most selective of recurrent cases. LigAmp had slightly better area under the receiver operator characteristic curve (P = 0.09) than light microscopy correctly predicting 9 of 15 recurrent tumors. There were 6 false negative cases and 26 false positive results. No statistically significant distinctions were observed in cancer-specific or overall survival in this limited cohort. Conclusions: Ligamp provides quantifiable, sensitive detection of mutant DNA in histologically normal margins. Detection of mutant species in margins may identify patients at risk of local recurrence. (Clin Cancer Res 2009;15(24):7658-65)