A characteristic of cancer development is the acquisition of genomic instability, which results from the inaccurate repair of DNA damage. Among double-strand break repair mechanisms induced by oncogenic stress, the highly mutagenic theta-mediated end-joining (TMEJ) pathway, which requires DNA polymerase theta (POLθ) encoded by the POLQ gene, has been shown to be overexpressed in several human cancers. However, little is known regarding the regulatory mechanisms of TMEJ and the consequence of its dysregulation. In this study, we combined a bioinformatics approach exploring both Molecular Taxonomy of Breast Cancer International Consortium and The Cancer Genome Atlas databases with CRISPR/Cas9-mediated depletion of the zinc finger E-box binding homeobox 1 (ZEB1) in claudin-low tumor cells or forced expression of ZEB1 in basal-like tumor cells, two triple-negative breast cancer (TNBC) subtypes, to demonstrate that ZEB1 represses POLQ expression. ZEB1, a master epithelial-to-mesenchymal transition–inducing transcription factor, interacted directly with the POLQ promoter. Moreover, downregulation of POLQ by ZEB1 fostered micronuclei formation in TNBC tumor cell lines. Consequently, ZEB1 expression prevented TMEJ activity, with a major impact on genome integrity. In conclusion, we showed that ZEB1 directly inhibits the expression of POLQ and, therefore, TMEJ activity, controlling both stability and integrity of breast cancer cell genomes. Significance: These findings uncover an original mechanism of TMEJ regulation, highlighting ZEB1 as a key player in genome stability during cancer progression via its repression of POLQ. See related commentary by Carvajal-Maldonado and Wood, p. 1441

Despite the ample improvements of CRC molecular landscape, the therapeutic options still rely on conventional chemotherapy-based regimens for early disease, and few targeted agents are recommended for clinical use in the metastatic setting. Moreover, the impact of cytotoxic, targeted agents, and immunotherapy combinations in the metastatic scenario is not fully satisfactory, especially the outcomes for patients who develop resistance to these treatments need to be improved. Here, we examine the opportunity to consider therapeutic agents targeting DNA repair and DNA replication stress response as strategies to exploit genetic or functional defects in the DNA damage response (DDR) pathways through synthetic lethal mechanisms, still not explored in CRC. These include the multiple actors involved in the repair of DNA double-strand breaks (DSBs) through homologous recombination (HR), classical non-homologous end joining (NHEJ), and microhomology-mediated end-joining (MMEJ), inhibitors of the base excision repair (BER) protein poly (ADP-ribose) polymerase (PARP), as well as inhibitors of the DNA damage kinases ataxia-telangiectasia and Rad3 related (ATR), CHK1, WEE1, and ataxia-telangiectasia mutated (ATM). We also review the biomarkers that guide the use of these agents, and current clinical trials with targeted DDR therapies.

Choriocarcinoma in neonates and infants (N‐CC) is an extremely rare, but aggressive cancer, frequently observed with concomitant maternal disease. A retrospective, bi‐national study of patients treated in France and Poland for infantile choriocarcinoma analysed eight cases of N‐CC, median age of 6 weeks. All tumours were diffuse. Six patients received a platinum‐based regimen, and five had delayed surgery on residual distant tumour sites. At the end of follow‐up, four patients were in complete remission and four had died of the disease. In all but two cases, mothers had simultaneous metastatic choriocarcinoma. Even if the outcome remains poor, patients could be cured with multimodal therapy.

Differentiating benign from malignant extrahepatic biliary strictures remains a diagnostic challenge, despite advances in sampling techniques and ancillary tests. Next-generation sequencing (NGS) may improve diagnostic performance and enable essential molecular profiling for malignancies. We aimed to assess the diagnostic performance of targeted NGS compared to cytohistology and fluorescence in situ hybridization (FISH), using samples exclusively collected via optimized single-operator cholangioscopy. We prospectively enrolled 104 patients with extrahepatic biliary strictures or suspected cholangiocarcinoma. A definitive diagnosis was established through cytohistology and clinical follow-up. In total, 445 samples (265 brushings and 180 biopsies) were collected. Targeted DNA sequencing was performed using a custom-designed 50-gene panel. FISH was retrospectively performed in a subgroup of 42 patients. The diagnostic performance of all three modalities was compared. NGS achieved a sensitivity of 82.2% for malignancy, significantly higher than cytohistology alone (59.2%, p = 1.9x10^-3). Combining both modalities increased sensitivity to 89.5% (p = 4.1x10^-2). In the 42-patient subgroup, combining NGS and cytohistology achieved 97.2% sensitivity, superior to cytohistology (66.7%), FISH (81.2%), the combination of cytohistology and FISH (86.1%) and NGS alone (86.1%). Among malignant cases, NGS succeeded in 96.1%, enabling early molecular profiling for these patients. The combination of cytohistology and NGS significantly improves diagnostic performance for cholangiocarcinoma in patients with extrahepatic biliary strictures using specimens obtained via single-operator cholangioscopy. This approach also enables early molecular profiling of low-cellularity specimens and may reduce diagnostic delays while optimizing therapeutic decision-making. Differentiating benign from malignant extrahepatic biliary strictures remains a major clinical challenge, justifying the need for more sensitive and specific diagnostic tools beyond conventional cytohistology. Our findings show that combining next-generation sequencing with cytohistology significantly improves diagnostic performance, enables early molecular profiling, and is easily applicable in clinical laboratories. These results are especially relevant for patients with suspected cholangiocarcinoma and patients with primary sclerosing cholangitis, where timely and accurate diagnosis is critical and often difficult. Integrating next-generation sequencing into routine diagnostic workflows could reduce diagnostic delays and guide therapeutic decisions in patients with biliary tract lesions.