Andrea Gabusi1, Davide Bartolomeo Gissi2, Achille Tarsitano3, Sofia Asioli4, Claudio Marchetti5, Lucio Montebugnoli6, Maria Pia Foschini7, Luca Morandi8. 1. PhD Student, Section of Oral Science, Department of Biomedical and Neuromuscular Sciences, University of Bologna, Bologna, Italy. 2. Research Fellow, Section of Oral Science, Department of Biomedical and Neuromuscular Sciences, University of Bologna, Bologna, Italy. 3. Researcher, Unit of Maxillofacial Surgery, S Orsola Hospital, Bologna, Italy. 4. Researcher, Department of Biomedical and Neuromotor Sciences, Section of Anatomic Pathology "M. Malpighi", Bellaria Hospital, Bologna, Italy. 5. Professor, Head of Unit of Maxillofacial Surgery, S Orsola Hospital, Bologna, Italy. 6. Professor, Head of Section of Oral Science, Department of Biomedical and Neuromuscular Sciences, University of Bologna, Bologna, Italy. 7. Professor, Department of Biomedical and Neuromotor Sciences, Head of Section of Anatomic Pathology "M. Malpighi", Bellaria Hospital, Bologna, Italy. 8. Research Laboratory Technical Director, Department of Biomedical and Neuromotor Sciences, Section of Anatomic Pathology "M. Malpighi", Bellaria Hospital, Bologna, Italy. Electronic address: luca.morandi2@unibo.it.
Abstract
PURPOSE: Improvements in sequencing technologies have shown that genetic differences among neoplastic cells can reflect clonal expansion. Intratumor heterogeneity (ITH) has been suggested to explain differences in prognosis and treatment response, indicating that personalized medicine is the goal of the future. This study evaluated ITH in 5 patients with recurrent metastatic oral squamous cell carcinoma (OSCC) and tracked the evolution from non-neoplastic tissue to neoplastic events developing after primary tumor formation. PATIENTS AND METHODS: Representative regions were macrodissected from specimens obtained from patients with OSCC of the tongue (n = 4) and floor of the mouth (n = 1). ITH and tumor evolution were explored by analyzing DNA mutations disclosed by next-generation sequencing of specific driver genes combined with changes in the mtDNA D-loop hypervariable region. Phylogenetic trees were generated employing MAFFT tool with UPGMA/Jukes-Cantor serving as the substitute model. RESULTS: High levels of heterogeneity were observed within and among tumors. ITH emerged as metastatic and recurrent events progressed, but the evolutionary patterns differed. In some patients, specific subclones persisted during tumor relapse. Neighboring tissue also was heterogeneous at the premalignant level. CONCLUSIONS: A multiregion approach yielded more representative data than did single samples when tumors were subjected to molecular investigation. Persistent mutations that might be targeted by individualized medicine were thus exposed. Mitochondrial DNA is a useful adjunct tool when studying the phylogenetic evolution of subclones. The clinical implications of "field" heterogeneity should be studied in depth.
PURPOSE: Improvements in sequencing technologies have shown that genetic differences among neoplastic cells can reflect clonal expansion. Intratumor heterogeneity (ITH) has been suggested to explain differences in prognosis and treatment response, indicating that personalized medicine is the goal of the future. This study evaluated ITH in 5 patients with recurrent metastatic oral squamous cell carcinoma (OSCC) and tracked the evolution from non-neoplastic tissue to neoplastic events developing after primary tumor formation. PATIENTS AND METHODS: Representative regions were macrodissected from specimens obtained from patients with OSCC of the tongue (n = 4) and floor of the mouth (n = 1). ITH and tumor evolution were explored by analyzing DNA mutations disclosed by next-generation sequencing of specific driver genes combined with changes in the mtDNA D-loop hypervariable region. Phylogenetic trees were generated employing MAFFT tool with UPGMA/Jukes-Cantor serving as the substitute model. RESULTS: High levels of heterogeneity were observed within and among tumors. ITH emerged as metastatic and recurrent events progressed, but the evolutionary patterns differed. In some patients, specific subclones persisted during tumor relapse. Neighboring tissue also was heterogeneous at the premalignant level. CONCLUSIONS: A multiregion approach yielded more representative data than did single samples when tumors were subjected to molecular investigation. Persistent mutations that might be targeted by individualized medicine were thus exposed. Mitochondrial DNA is a useful adjunct tool when studying the phylogenetic evolution of subclones. The clinical implications of "field" heterogeneity should be studied in depth.