Intratumor genetic heterogeneity in squamous cell carcinoma of the oral cavity

Background We sought to evaluate intratumor heterogeneity in squamous cell carcinoma of the oral cavity (OCC) and specifically determine the effect of physical separation and histologic differentiation within the same tumor. Methods We performed whole exome sequencing on five biopsy sites-two from well-differentiated, two from poorly differentiated regions, and one from normal parenchyma-from five primary OCC specimens. Results We found high levels of intratumor heterogeneity and, in four primary tumors, identified only 0 to 2 identical mutations in all subsites. We found that the heterogeneity inversely correlated with physical separation and that pairs of well-differentiated samples were more similar to each other than analogous poorly differentiated specimens. Only TP53 mutations, but not other purported "driver mutations" in head and neck squamous cell carcinoma, were found in multiple biopsy sites. Conclusion These data highlight the challenges to characterization of the mutational landscape of OCC with single site biopsy and have implications for personalized medicine.