A considerable proportion of tumors exhibit aneuploid karyotypes, likely resulting from the progressive loss of chromosomes after whole-genome duplication. Here, by using isogenic diploid and near-tetraploid (4N) single-cell-derived clones from the same parental cell lines, we aimed at exploring how polyploidization affects cellular functions and how tetraploidy generates chromosome instability. Gene expression profiling in 4N clones revealed a significant enrichment of transcripts involved in cell cycle and DNA replication. Increased levels of replication stress in 4N cells resulted in DNA damage, impaired proliferation caused by a cell cycle delay during S phase, and higher sensitivity to S phase checkpoint inhibitors. In fact, increased levels of replication stress were also observed in nontransformed, proliferative posttetraploid RPE1 cells. Additionally, replication stress promoted higher levels of intercellular genomic heterogeneity and ongoing genomic instability, which could be explained by high rates of mitotic defects, and was alleviated by the supplementation of exogenous nucleosides. Finally, our data found that 4N cancer cells displayed increased migratory and invasive capacity, both in vitro and in primary colorectal tumors, indicating that tetraploidy can promote aggressive cancer cell behavior.-Wangsa, D., Quintanilla, I., Torabi, K., Vila-Casadesús, M., Ercilla, A., Klus, G., Yuce, Z., Galofré, C., Cuatrecasas, M., Lozano, J. J., Agell, N., Cimini, D., Castells, A., Ried, T., Camps, J. Near-tetraploid cancer cells show chromosome instability triggered by replication stress and exhibit enhanced invasiveness.

for the Gastrointestinal Oncology Group of the Spanish Gastroenterological Association 1 BACKGROUND: Colorectal cancers (CRCs) that have microsatellite instability (MSI) and mutL homolog 1 (MLH1) immunoloss are observed in 3 clinical scenarios: Lynch syndrome (LS), sporadic MSI CRC, and Lynch-like syndrome (LLS). v-Raf murine sarcoma viral oncogene homolog B1 (BRAF) mutational analysis is used to differentiate LS from sporadic MSI CRC. The role of MLH1 promoter methylation status for the differential diagnosis of these clinical forms is not well established. The objectives of this study were: 1) to analyze MLH1 promoter methylation in MLH1-deficient CRCs by pyrosequencing, and 2) to assess its role in the differential diagnosis of MLH1-deficient CRCs. METHODS: In total, 165 CRCs were analyzed, including LS (n 5 19), MSI BRAF-mutated CRC (n 5 37), MSI BRAF wild-type CRC (n 5 60), and a control group of CRCs without MSI (microsatellite stable [MSS] CRC; n 5 49). MLH1 promoter methylation status was analyzed by pyrosequencing, and the ability of different strategies to identify LS was assessed. RESULTS: The average 6 standard deviation methylation in LS (9% 6 7%) was significantly lower than that in MSI BRAF-mutated CRC (42% 6 17%; P <.001) and in MSI BRAF wild-type CRC (25% 6 19%; P 5.002). Somatic MLH1 hypermethylation was detected in 3 patients (15.8%) with LS, in 34 patients (91.9%) with MSI BRAF-mutated CRC, and in 37 patients (61.7%) with MSI BRAF wild-type tumors. Patients with MSI BRAF wild-type, unmethylated tumors (ie, LLS) had a stronger family history of CRC than those who had tumors with MLH1 methylation (P <.05). The sensitivity for ruling out LS was 100% for BRAF analysis, 84.2% for MLH1 methylation analysis, and 84.2% for the combination of both analyses. CONCLUSIONS: Somatic MLH1 promoter methylation occurs in up to 15% of LS CRCs. Somatic BRAF analysis is the most sensitive strategy for ruling out LS. Patients who have CRCs with loss of MLH1 protein expression and neither BRAF mutation nor MLH1 methylation resemble patients with LS. Cancer 2015;121:1395-404.

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