MRE11 Deficiency Occurs in a Small Group of Cancers from Various Different Tumor Entities

Background/Objectives: The double-strand break repair protein MRE11 forms the core of the MRE11/RAD50/NBS1 (MRN) complex. Cancers with reduced MRE11 expression have been suggested to be more sensitive to radio-chemotherapy and may be subject to synthetic lethality. The aim of this study was to assess the prevalence of MRE11 deficiency and the potential role and clinical significance of elevated and/or reduced MRE11 expression in human cancer. Methods: A tissue microarray containing 14,966 samples from 134 different tumor entities was analyzed for MRE11 by immunohistochemistry. Results: In normal tissues, strong nuclear MRE11 staining occurred in almost all cell types. In cancers, nuclear MRE11 staining was strong in 11,797 (91.0%), moderate in 1018 (7.9%), weak in 86 (0.7%), and completely absent (MRE11 deficiency) in 55 (0.4%) of 12,956 informative tumor samples. Only six tumor entities had more than one MRE11-deficient cases including hepatocellular carcinoma (9 of 193), intestinal type gastric adenocarcinoma (4 of 208), endometrioid endometrial carcinoma (5 of 268), pulmonary adenocarcinoma (2 of 165), colorectal adenocarcinoma (CRC, 16 of 2183), and clear cell renal cell carcinoma (ccRCC, 7 of 1011). Reduced MRE11 staining was associated with mismatch repair deficiency (dMMR) in CRC and in gastric adenocarcinoma (p < 0.0001 each), advanced pT stage (p = 0.0003) and L1 status (p = 0.0019) in testicular seminoma, high grade (p < 0.05), advanced pT (p < 0.0001), and high UICC stage (p = 0.0014) in ccRCC, advanced pT stage in high-grade serous ovarian carcinoma (p = 0.0396), and nodal metastases in papillary thyroid cancer (p = 0.0332). Conclusions: MRE11 is highly expressed in most cancers. Reduced MRE11 expression is associated with aggressive phenotype in multiple cancer types. The potential to exploit MRE11 deficiency as a target for synthetic lethality deserves to be further explored.