The Evolution of Clinically Aggressive Triple-Negative Breast Cancer Shows a Large Mutational Diversity and Early Metastasis to Lymph Nodes

In triple-negative breast cancer (TNBC), only 30% of patients treated with neoadjuvant chemotherapy achieve a pathological complete response after treatment and more than 90% die due to metastasis formation. The diverse clinical responses and metastatic developments are attributed to extensive intrapatient genetic heterogeneity and tumor evolution acting on this neoplasm. In this work, we aimed to evaluate genomic alterations and tumor evolution in TNBC patients with aggressive disease. We sequenced the whole exome of 16 lesions from four patients who did not respond to therapy, and took several follow-up samples, including samples from tumors before and after treatment, as well as from the lymph nodes and skin metastases. We found substantial intrapatient genetic heterogeneity, with a variable tumor mutational composition. Early truncal events were MCL1 amplifications. Metastatic lesions had deletions in RB1 and PTEN, along with TERT, AKT2, and CCNE1 amplifications. Mutational signatures 06 and 12 were mainly detected in skin metastases and lymph nodes. According to phylogenetic analysis, the lymph node metastases occurred at an early stage of TNBC development. Finally, each patient had three to eight candidate driving mutations for targeted treatments. This study delves into the genomic complexity and the phylogenetic and evolutionary development of aggressive TNBC, supporting early metastatic development, and identifies specific genetic alterations associated with a response to targeted therapies.

Comprehensive Genomic Profile of Heterogeneous Long Follow-Up Triple-Negative Breast Cancer and Its Clinical Characteristics Shows DNA Repair Deficiency Has Better Prognostic

Triple-negative breast cancer (TNBC) presents a marked diversity at the molecular level, which promotes a clinical heterogeneity that further complicates treatment. We performed a detailed whole exome sequencing profile of 29 Mexican patients with long follow-up TNBC to identify genomic alterations associated with overall survival (OS), disease-free survival (DFS), and pathologic complete response (PCR), with the aim to define their role as molecular predictive factors of treatment response and prognosis. We detected 31 driver genes with pathogenic mutations in TP53 (53%), BRCA1/2 (27%), CDKN1B (9%), PIK3CA (9%), and PTEN (9%), and 16 operative mutational signatures. Moreover, tumors with mutations in BRCA1/2 showed a trend of sensitivity to platinum salts. We found an association between deficiency in DNA repair and surveillance genes and DFS. Across all analyzed tumors we consistently found a heterogeneous molecular complexity in terms of allelic composition and operative mutational processes, which hampered the definition of molecular traits with clinical utility. This work contributes to the elucidation of the global molecular alterations of TNBC by providing accurate genomic data that may help forthcoming studies to improve treatment and survival. This is the first study that integrates genomic alterations with a long follow-up of clinical variables in a Latin American population that is an underrepresented ethnicity in most of the genomic studies.

Abstract 1240: Comprehensive analysis of germline variants in Mexican patients with hereditary breast and ovarian cancer susceptibility

Hereditary breast and ovarian cancer syndrome (HBOC) is an autosomal dominant disease that represents approximately 5-10% of all patients with breast cancer. This syndrome is mainly associated to high-risk pathogenic alleles in BRCA1 and BRCA2 genes, but only for 25% of HBOC cases. This work aimed to find new pathogenic alleles in a panel of 143 cancer-predisposing genes in 300 Mexican cancer patients with suspicion of HBOC and 31 non-cancer patients with a severe family history of cancer, using massive parallel sequencing. We found 15% (45/300) patients with pathogenic variants in the group of cancer patients; 12% (35/300) harbored variants with unknown clinical significance (VUS) and 73% (220/300) were negative. The non-cancer group had a 32% (10/31) of patients with pathogenic variants, 3% (1/31) had VUS and 65% (20/31) were negative. Moreover, the most recurrent mutation was the Mexican founder deletion of exons 9-12 in BRCA1, found in 5 of 16 cancer patients with alterations in this gene. Private or rare VUS variants with potential impact at protein level were found in 22 genes, being CHEK2 the one with most VUS (6/39). Noteworthy, our results show for the first time in the Mexican population an equal contribution of pathogenic alleles in other susceptibility cancer genes (50%) as in BRCA1/2 (50%). This highlights the high locus heterogeneity of HBOC and the necessity of expanding genetic tests for this disease to broader gene panels. Further studies need to be conducted to define the clinical impact of the pathogenic alleles and VUS identified.

Citation Format: Felipe Vaca-Paniagua, Rosalía Quezada-Urban, Clara E. Díaz-Velásquez, Rina Gitler, María P. Rojo-Castillo, Max Sirota-Toporek, Andrea Figueroa-Morales, Oscar Moreno-García, Lizbeth García Esquivel, Gabriela Torres-Mejía, Michael Dean, Ivan Delgado-Enciso, Héctor Ochoa-Díaz-López, Fernando Rodriguez-León, Virginia Jan, Victor H. Hugo Garzón-Barrientos, Pablo Ruiz-Flores, Perla K. Espino-Silva, Jorge Haro-Santa Cruz, Héctor Martínez-Gregorio, Ernesto Rojas-Jiménez, Rosa M. Álvarez-Gómez, Luis A. Herrera, Isabelle Romieu, Luis I. Terrazas, Yolanda I. Chirino, Cecilia Frecha, Javier Oliver, Sandra Perdomo. Comprehensive analysis of germline variants in Mexican patients with hereditary breast and ovarian cancer susceptibility [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1240.