Carla Colombo1,2, Marina Muzza1,2,3, Maria Carla Proverbio2, Delfina Tosi4,5, Davide Soranna6, Chiara Pesenti2,7, Stefania Rossi4, Valentina Cirello1, Simone De Leo1,2, Nicola Fusco7,8, Monica Miozzo2,7, Gaetano Bulfamante4,5, Leonardo Vicentini9, Stefano Ferrero7,8, Antonella Zambon10, Silvia Tabano2,7, Laura Fugazzola1,2. 1. 1 Division of Endocrine and Metabolic Diseases, IRCCS Istituto Auxologico Italiano, Milan, Italy. 2. 2 Department of Pathophysiology and Transplantation, Università degli Studi di Milano, Milan, Italy. 3. 3 Endocrine Unit, Fondazione IRCCS Ca' Granda-Ospedale Maggiore Policlinico, Milan, Italy. 4. 4 Unit of Pathology, ASST Santi Paolo e Carlo, Milan, Italy. 5. 5 Department of Health Sciences, Università degli Studi di Milano, Milan, Italy. 6. 6 IRCCS Istituto Auxologico Italiano, Milan, Italy. 7. 8 Division of Pathology, Fondazione IRCCS Ca' Granda-Ospedale Maggiore Policlinico, Milan, Italy. 8. 9 Department of Biomedical, Surgical, and Dental Sciences, Università degli Studi di Milano, Milan, Italy. 9. 10 Endocrine Surgery Unit, IRCCS Istituto Auxologico Italiano, Milan, Italy. 10. 7 Department of Statistics and Quantitative Methods, University of Milano-Bicocca, Milan, Italy.
Abstract
BACKGROUND: The need to integrate the classification of cancer with information on the genetic pattern has emerged in recent years for several tumors. METHODS: The genomic background of a large series of 208 papillary thyroid cancers (PTC) followed at a single center was analyzed by a custom MassARRAY genotyping platform, which allows the simultaneous detection of 19 common genetic alterations, including point mutations and fusions. RESULTS: Of the PTCs investigated, 71% were found to have pathognomonic genetic findings, with BRAFV600E and TERT promoter mutations being the most frequent monoallelic alterations (42% and 23.5%, respectively), followed by RET/PTC fusions. In 19.2% of cases, two or more point mutations were found, and the co-occurrence of a fusion with one or more point mutation(s) was also observed. Coexisting BRAFV600E and TERT promoter mutations were detected in a subgroup of aggressive PTCs (12%). A correlation between several aggressive features and mutation density was found, regardless of the type of association (i.e., only point mutations, or point mutations and fusions). Importantly, Kaplan-Meier curves demonstrated that mutation density significantly correlated with a higher risk of persistent disease. In most cases, the evaluation of the allelic frequencies normalized for the cancer cell content indicated the presence of the monoallelic mutation in virtually all tumor cells. A minority of cases was found to harbor low allelic frequencies, consistent with the presence of the mutations in a small subset of cancer cells, thus indicating tumor heterogeneity. Consistently, the presence of coexisting genetic alterations with different allelic frequencies in some tumors suggests that PTC can be formed by clones/subclones with different mutational profiles. CONCLUSIONS: A large mono-institutional series of PTCs was fully genotyped by means of a cost- and time-effective customized panel, revealing a strong impact of mutation density and genetic heterogeneity on the clinical features and on disease outcomes, indicating that an accurate risk stratification of thyroid cancer cannot rely on the analysis of a single genetic event. Finally, the heterogeneity found in some tumors warrants attention, since the occurrence of this phenomenon is likely to affect response to targeted therapies.
BACKGROUND: The need to integrate the classification of cancer with information on the genetic pattern has emerged in recent years for several tumors. METHODS: The genomic background of a large series of 208 papillary thyroid cancers (PTC) followed at a single center was analyzed by a custom MassARRAY genotyping platform, which allows the simultaneous detection of 19 common genetic alterations, including point mutations and fusions. RESULTS: Of the PTCs investigated, 71% were found to have pathognomonic genetic findings, with BRAFV600E and TERT promoter mutations being the most frequent monoallelic alterations (42% and 23.5%, respectively), followed by RET/PTC fusions. In 19.2% of cases, two or more point mutations were found, and the co-occurrence of a fusion with one or more point mutation(s) was also observed. Coexisting BRAFV600E and TERT promoter mutations were detected in a subgroup of aggressive PTCs (12%). A correlation between several aggressive features and mutation density was found, regardless of the type of association (i.e., only point mutations, or point mutations and fusions). Importantly, Kaplan-Meier curves demonstrated that mutation density significantly correlated with a higher risk of persistent disease. In most cases, the evaluation of the allelic frequencies normalized for the cancer cell content indicated the presence of the monoallelic mutation in virtually all tumor cells. A minority of cases was found to harbor low allelic frequencies, consistent with the presence of the mutations in a small subset of cancer cells, thus indicating tumor heterogeneity. Consistently, the presence of coexisting genetic alterations with different allelic frequencies in some tumors suggests that PTC can be formed by clones/subclones with different mutational profiles. CONCLUSIONS: A large mono-institutional series of PTCs was fully genotyped by means of a cost- and time-effective customized panel, revealing a strong impact of mutation density and genetic heterogeneity on the clinical features and on disease outcomes, indicating that an accurate risk stratification of thyroid cancer cannot rely on the analysis of a single genetic event. Finally, the heterogeneity found in some tumors warrants attention, since the occurrence of this phenomenon is likely to affect response to targeted therapies.