PD-L1 expression, tumor-infiltrating lymphocytes, mismatch repair deficiency, EGFR alteration and HPV infection in sinonasal squamous cell carcinoma.

The antitumor efficacies of immune checkpoint inhibitors (ICIs) and the usefulness of potential predictive markers such as programmed death-ligand 1 (PD-L1) expression, density of tumor-infiltrating lymphocytes (TILs) and microsatellite instability (MSI) in sinonasal squamous cell carcinoma (SNSCC) have not been fully elucidated. We retrospectively analyzed 131 SNSCCs with immunohistochemistry for PD-L1 expression, TIL subpopulations and loss of mismatch repair (MMR) proteins as a surrogate for MSI-high. We also comprehensively evaluated the mutual relationships among these immuno-markers, high-risk human papillomavirus (HPV) infection, epidermal growth factor receptor (EGFR) gene status, and KRAS mutation. PD-L1 expression (tumor proportion score ≥ 1%) was detected in 60 (45.8%) SNSCC cases and was significantly associated with worse overall survival (OS) (p = 0.0240). High density of cluster of differentiation 8 (CD8)-positive TILs was significantly associated with better progression-free survival (PFS) (p = 0.0368), and high density of forkhead box protein P3-positive TILs was significantly associated with better PFS and OS (p = 0.0007 and 0.0143, respectively). With respect to the combination of CD8 + TIL and PD-L1 expression, the high-CD8/PD-L1-negative group showed the most favorable prognosis, whereas the low-CD8/PD-L1-positive group showed the worst prognosis. MMR loss was detected in 3 (2.3%) of the 131 cases. HPV infection (6.1%), EGFR mutation (14.5%), EGFR copy number gain (26%), and MMR loss were essentially mutually exclusive; patients in these molecular groups showed significant differences in prognosis but not in the degree of PD-L1 expression or TILs. Among the nine ICI-treated patients, three (33.3%) were responders, and the EGFR-wild type cases (n = 7) showed better clinical responses to an ICI compared to the EGFR-mutant cases (n = 2). Among the patients with residual/recurrent EGFR-wild type tumors (n = 43), ICI treatment significantly improved OS (p = 0.0281). The results suggest that the evaluation of immuno-markers and molecular subclassification may be helpful for prognostic prediction and selecting an individualized therapeutic strategy for patients with SNSCC.

Molecular basis of the dual role of the Mlh1-Mlh3 endonuclease in MMR and in meiotic crossover formation.

In budding yeast, the MutL homolog heterodimer Mlh1-Mlh3 (MutLγ) plays a central role in the formation of meiotic crossovers. It is also involved in the repair of a subset of mismatches besides the main mismatch repair (MMR) endonuclease Mlh1-Pms1 (MutLα). The heterodimer interface and endonuclease sites of MutLγ and MutLα are located in their C-terminal domain (CTD). The molecular basis of MutLγ's dual roles in MMR and meiosis is not known. To better understand the specificity of MutLγ, we characterized the crystal structure of Saccharomyces cerevisiae MutLγ(CTD). Although MutLγ(CTD) presents overall similarities with MutLα(CTD), it harbors some rearrangement of the surface surrounding the active site, which indicates altered substrate preference. The last amino acids of Mlh1 participate in the Mlh3 endonuclease site as previously reported for Pms1. We characterized mlh1 alleles and showed a critical role of this Mlh1 extreme C terminus both in MMR and in meiotic recombination. We showed that the MutLγ(CTD) preferentially binds Holliday junctions, contrary to MutLα(CTD). We characterized Mlh3 positions on the N-terminal domain (NTD) and CTD that could contribute to the positioning of the NTD close to the CTD in the context of the full-length MutLγ. Finally, crystal packing revealed an assembly of MutLγ(CTD) molecules in filament structures. Mutation at the corresponding interfaces reduced crossover formation, suggesting that these superstructures may contribute to the oligomer formation proposed for MutLγ. This study defines clear divergent features between the MutL homologs and identifies, at the molecular level, their specialization toward MMR or meiotic recombination functions.

OTUB1 stabilizes mismatch repair protein MSH2 by blocking ubiquitination.

DNA mismatch repair (MMR) maintains genome stability primarily by correcting replication errors. MMR deficiency can lead to cancer development and bolsters cancer cell resistance to chemotherapy. However, recent studies have shown that checkpoint blockade therapy is effective in MMR-deficient cancers, thus the ability to identify cancer etiology would greatly benefit cancer treatment. MutS homolog 2 (MSH2) is an obligate subunit of mismatch recognition proteins MutSα (MSH2-MSH6) and MutSß (MSH2-MSH3). Precise regulation of MSH2 is critical, as either over- or underexpression of MSH2 results in an increased mutation frequency. The mechanism by which cells maintain MSH2 proteostasis is unknown. Using functional ubiquitination and deubiquitination assays, we show that the ovarian tumor (OTU) family deubiquitinase ubiquitin aldehyde binding 1 (OTUB1) inhibits MSH2 ubiquitination by blocking the E2 ligase ubiquitin transfer activity. Depleting OTUB1 in cells promotes the ubiquitination and subsequent degradation of MSH2, leading to greater mutation frequency and cellular resistance to genotoxic agents, including the common chemotherapy agents N-methyl-N'-nitro-N-nitrosoguanidine and cisplatin. Taken together, our data identify OTUB1 as an important regulator of MSH2 stability and provide evidence that OTUB1 is a potential biomarker for cancer etiology and therapy.

Dynamics of genomic and immune responses during primary immunotherapy resistance in mismatch repair-deficient tumors.

Mismatch repair-deficient (dMMR) cancers generate a substantial number of immunogenic neoantigens, rendering them sensitive to immunotherapy. Yet, there is considerable variability in responses, and roughly one-half of dMMR cancers are refractory to immunotherapy. Here we study a patient with dMMR lung cancer refractory to immunotherapy. The tumor exhibited typical dMMR molecular features, including exceptionally high frameshift insertions and deletions (indels). Despite the treatment inducing abundant intratumoral T-cell infiltrates, it failed to elicit tumor regression, pointing to the T cells lacking cytotoxic activity. A post-treatment tumor demonstrated compound heterozygous frameshift deletions located upstream of the kinase domain in the gene encoding JAK1 protein, down-regulation of JAK1 and mediators of its signal transduction, and total loss of JAK1 phosphorylation. Importantly, one of the JAK1 mutations, despite not being detected in the pretreatment tumor, was found at low variant allele frequency in the pretreatment circulating tumor DNA, suggesting clonal selection of the mutation. To our knowledge, this report provides the most detailed look yet at defective JAK1 signaling in the context of dMMR and immunotherapy resistance. Together with observations of JAK1 frameshift indels being enriched in dMMR compared with MMR-proficient tumors, our findings demonstrate the critical function of JAK1 in immunological surveillance of dMMR cancer.

Mitochondrial behavior during nuclear and mitochondrial DNA repair in Trypanosoma cruzi epimastigotes.

Different genotoxic agents can lead to DNA single- and double-strand breaks, base modification and oxidation. As most living organisms, Trypanosoma cruzi is subjected to oxidative stress during its life cycle; thus, DNA repair is essential for parasite survival and establishment of infection. The mitochondrion plays important roles beyond the production of ATP. For example, it is a source of signaling molecules, such as the superoxide anion and H2O2. Since T. cruzi has only one mitochondrion, the integrity of this organelle is pivotal for parasite viability. H2O2 and methyl methanesulfonate cause DNA lesions in T. cruzi that are repaired by different DNA repair pathways. Herein, we evaluate mitochondrial involvement during the repair of nuclear and mitochondrial DNA in T. cruzi epimastigotes incubated with these two genotoxic agents under conditions that induce repairable DNA damage. Overall, in both treatments, an increase in oxygen consumption rates and in mitochondrial H2O2 release was observed, as well as maintenance of ATP levels compared to control. Interestingly, these changes coincided with DNA repair kinetics, suggesting the importance of the mitochondrion for this energy-consuming process.

DNA Mismatch Repair-deficient Endometrial Carcinosarcomas Portend Distinct Clinical, Morphologic, and Molecular Features Compared With Traditional Carcinosarcomas.

Uterine carcinosarcomas (UCSs) are aggressive neoplasms composed of high-grade malignant epithelial and mesenchymal elements with most (∼90%) showing TP53 abnormalities. A subset, however, shows mismatch repair deficiency (MMR-D). We sought to describe their clinical, morphologic, and molecular features. Clinicopathologic data of MMR-D UCSs were recorded including age, stage, follow-up, mismatch repair and p53 immunohistochemistry (IHC), MLH1 promoter methylation status, and germline alterations, TP53 mutation status, microsatellite instability and mutational burden by massively parallel sequencing. Seventeen (6.2%) MMR-D were identified among 276 UCSs. Of MMR-D UCSs, the median age was 60 years. mismatch repair IHC loss is as follows: MLH1/PMS2 65%, MSH2/MSH6 18%, MSH6 12%, and PMS2 6%. MLH1 promoter methylation and Lynch syndrome was identified in 47% and 12% of cases, respectively. Cases with p53 IHC showed the following patterns: wild-type 70%, aberrant 20%, and equivocal 10%. Of cases with sequencing, 88% were hypermutated and microsatellite instability high. High-grade endometrioid, undifferentiated, and clear cell carcinoma was present in 53%, 41%, and 6% of cases, respectively and 47% also showed a low-grade endometrioid component. Most patients presented at an early stage (67%) and upon follow-up, 18% died of disease, 65% showed no evidence of disease, while 18% are alive with disease. Patients with MMR-D UCS are younger than the reported median age (70 y) for traditional UCS and most do not show p53 abnormalities. Low-grade endometrioid and undifferentiated carcinoma were seen in approximately half of all cases. Although UCSs have a high tendency for early extrauterine spread, most patients in our cohort presented at an early stage and at follow-up were no evidence of disease. MMR-D UCSs display distinct clinical, morphologic, and molecular features compared with traditional UCSs.

POLE Mutation Spectra Are Shaped by the Mutant Allele Identity, Its Abundance, and Mismatch Repair Status.

Human tumors with exonuclease domain mutations in the gene encoding DNA polymerase ε (POLE) have incredibly high mutation burdens. These errors arise in four unique mutation signatures occurring in different relative amounts, the etiologies of which remain poorly understood. We used CRISPR-Cas9 to engineer human cell lines expressing POLE tumor variants, with and without mismatch repair (MMR). Whole-exome sequencing of these cells after defined numbers of population doublings permitted analysis of nascent mutation accumulation. Unlike an exonuclease active site mutant that we previously characterized, POLE cancer mutants readily drive signature mutagenesis in the presence of functional MMR. Comparison of cell line and human patient data suggests that the relative abundance of mutation signatures partitions POLE tumors into distinct subgroups dependent on the nature of the POLE allele, its expression level, and MMR status. These results suggest that different POLE mutants have previously unappreciated differences in replication fidelity and mutagenesis.

Loss of DNA mismatch repair proteins in prostate cancer.

Recent studies have suggested an increased risk of prostate cancer in men with Lynch syndrome driven by germline mutations in mismatch repair (MMR) genes. However, the incidence and clinical implication of MMR deficiency in sporadic prostate cancers remain poorly understood. We immunohistochemically stained for MLH1, MSH2, MSH6, and PMS2 in a set of tissue microarray consisting of 220 radical prostatectomy specimens and evaluated the relationship between loss of their expression and available clinicopathological features. MLH1, MSH2, MSH6, and PMS2 were lost in 2 (0.9%), 6 (2.7%), 37 (16.8%), and 27 (12.3%) prostate cancers, respectively. Loss of at least 1 MMR protein was identified in 50 (22.7%) cases. There were no statistically significant associations between MMR deficiency and patient age, family history of prostate cancer, Gleason score, or pT/pN stage. Nonetheless, the levels of preoperative prostate-specific antigen (PSA) were significantly (P = .015) higher in patients with MMR deficiency (mean ±â€ŠSD: 9.12 ±â€Š9.01 ng/mL) than in those without abnormal MMR (5.76 ±â€Š3.17 ng/mL). There were 15 (6.8%) cases showing loss of at least 2 MMR proteins, which was not significantly associated with PSA level or tumor grade/stage. Additionally, 5 and 2 cases showed losses of at least 3 MMR proteins and all 4 proteins, respectively. Kaplan-Meier analysis revealed no significant associations between loss of MLH1 (P = .373), MSH2 (P = .348), MSH6 (P = .946), or PMS2 (P = .681), or at least 1 (P = .477), 2 (P = .486), or 3 (P = .352) MMR proteins and biochemical recurrence. Further analyses of the data on programmed death-ligand 1 (PD-L1) expression previously stained in the same set of tissue microarray demonstrated associations between loss of ≥2 MMR proteins and a higher rate of PD-L1 expression in cancer cells (17.2% vs 5.2%; P = .033) as well as between cases showing both loss of ≥1 MMR protein(s) and PD-L1 expression in tumor-infiltrating immune cells vs a higher risk of biochemical recurrence (P = .045). MMR protein loss was seen in a subset of prostate cancers. Interestingly, it was associated with significantly higher levels of PSA. Moreover, immunohistochemical detection of MMR proteins together with other proteins, such as PD-L1, might be helpful in predicting tumor recurrence following radical prostatectomy.

Long Survival and Prolonged Remission after Surgery and Chemotherapy in a Metastatic Mismatch Repair Deficient Pancreatic Neuroendocrine Carcinoma with MLH1/PMS2 Immunodeficiency and Minimal Microsatellite Shift.

Pancreatic neuroendocrine carcinomas (NECs) are rare and very aggressive neoplasms with dismal prognosis, especially when metastatic or with negative prognostic factors, such as vascular invasion. To the best of our knowledge, no case of pancreatic NEC with mismatch repair deficiency has been reported to date. We describe a 62-year-old patient who underwent pancreaticoduodenectomy for a NEC located in the pancreatic head, with peripancreatic lymph node metastases. Tumor necrosis was prominent and the Ki67 proliferative index was 60%. One year after the diagnosis, the patient experienced recurrence with a left supraclavicular lymph node metastasis, which was surgically removed, followed by standard cisplatin-etoposide chemotherapy. Neoplastic cells showed combined loss of expression of MLH1 and PMS2 in both primary tumor and lymph node metastasis. Microsatellite instability (MSI) test using a mononucleotide repeats pentaplex PCR (BAT-25, BAT-26, NR-21, NR-22, and NR-24) revealed minimal mononucleotide shifts showing deletion of less than 3 bp at NR-21, BAT-26, NR-24, and NR-22 loci. MLH1 methylation analysis revealed absence of the gene promoter methylation. BRAF and KRAS mutations were not detected. In gut, NECs' mismatch repair deficiency phenotype has been reported in about 10% of cases, and it represents an independent factor of more favorable outcome. Likewise, our patient is currently alive with a follow-up of more than 12 years after pancreaticoduodenectomy, by itself an unexpected finding for such an aggressive neoplasm.

Correlation of mismatch repair protein deficiency, PD-L1 and CD8 expression in high-grade urothelial carcinoma of the bladder.

Mismatch repair-deficient (d-MMR) tumours have been reported to show susceptibility to immune checkpoint inhibitors targeting programmed death-1/PD ligand-1 (PD-1/PD-L1). In this study, we sought to correlate the association of d-MMR, PD-L1 and CD8 expression in muscle invasive, high-grade urothelial carcinoma (HGUC) of bladder. A tissue microarray (TMA) was constructed from 201 cases and sequentially stained with PD-L1, CD8, MSH2, MSH6, MLH1 and PMS2. PD-L1 was assessed in tumour and immune cells. CD8 was assessed in a hotspot fashion with results averaged across cores. Loss of nuclear MMR expression on TMA sections was further assessed using corresponding whole tissue sections. d-MMR was identified in four cases (2%). The mean CD8 count was significantly higher in d-MMR tumours (10 vs 35, p=0.007) as was the proportion of PD-L1 positivity (75% vs 20%, p=0.031). d-MMR is uncommon in HGUC of bladder but shows strong correlation with cytotoxic T lymphocyte infiltration and PD-L1 tissue expression.

Canonical DNA non-homologous end-joining; capacity versus fidelity.

The significance of canonical DNA non-homologous end-joining (c-NHEJ) for DNA double strand break (DSB) repair has increased from lower organisms to higher eukaryotes, and plays the predominant role in human cells. Ku, the c-NHEJ end-binding component, binds DSBs with high efficiency enabling c-NHEJ to be the first choice DSB repair pathway, although alternative pathways can ensue after regulated steps to remove Ku. Indeed, radiation-induced DSBs are repaired rapidly in human cells. However, an important question is the fidelity with which radiation-induced DSBs are repaired, which is essential for assessing any harmful impacts caused by radiation exposure. Indeed, is compromised fidelity a price we pay for high capacity repair. Two subpathways of c-NHEJ have been revealed; a fast process that does not require nucleases or significant chromatin changes and a slower process that necessitates resection factors, and potentially more significant chromatin changes at the DSB. Recent studies have also shown that DSBs within transcriptionally active regions are repaired by specialised mechanisms, and the response at such DSBs encompasses a process of transcriptional arrest. Here, we consider the limitations of c-NHEJ that might result in DSB misrepair. We consider the common IR-induced misrepair events and discuss how they might arise via the distinct subpathways of c-NHEJ.

Differences in PD-L1-Expressing Macrophages and Immune Microenvironment in Testicular Germ Cell Tumors.

OBJECTIVES: To characterize the tumor microenvironment of testicular germ cell tumors (GCTs) using immunohistochemical markers. METHODS: Seventy-seven orchiectomies, including 36 nonmetastatic (NM) seminomas, 15 metastatic (M) seminomas, 13 nonmetastatic nonseminomatous germ cell tumors (NSGCTs), and 13 metastatic NSGCTs, were studied with PD-1, PD-L1, FOXP3, CD68, CD163, and mismatch repair (MMR) immunohistochemistry. FOXP3+ and PD-1+ tumor-infiltrating lymphocytes (TILs) and tumor-associated macrophages (TAMs) expressing CD68 and CD163 were enumerated. PDL-1 expression was evaluated on tumor cells and macrophages. RESULTS: GCTs primarily express PD-L1 on TAMs, except choriocarcinoma, where true tumor cell positivity was noted. Seminomas reveal increased intratumoral PD-L1+ TAMs compared with NSGCTs (P < .05). Activated TILs are increased in NM-seminomas compared with M-seminomas (P < .05). All GCTs retained MMR expression. CONCLUSIONS: Robust PD-L1+ TAMs are significantly expanded in seminomas compared with NSGCTs. Among all GCTs, only choriocarcinoma cells reveal true positivity for PD-L1. These findings expand the realm of potentially targeted treatments for GCTs.

Temozolomide-resistant Glioblastoma Depends on HDAC6 Activity Through Regulation of DNA Mismatch Repair.

BACKGROUND/AIM: Histone deacetylase 6 (HDAC6) is considered as one of the most promising targets in drug development for cancer therapy. Drug resistance is a major cause of treatment failure in many cancers including glioblastoma (GBM), the most lethal malignant tumor. The role of HDAC6 in GBM resistance and its underlying mechanisms have not been well elucidated. Herein, we investigated the function of HDAC6 in modulating GBM resistance. MATERIALS AND METHODS: The anticancer effects of four structurally distinct selective HDAC6 inhibitors were addressed using western blot, flow cytometry, CCK-8 assay, and CI in temozolomide (TMZ)-resistant GBM cells. RESULTS: We showed that HDAC6-selecitve inhibitors block activation of the EGFR and p53 pathways in TMZ-resistant GBM cells. Importantly, the inhibition of HDAC6 correlates with increased levels of MSH2 and MSH6, key DNA mismatch repair proteins, in TMZ-resistant GBM cells. In addition to the MSH, HDAC6 inhibitors decrease MGMT expression in TMZ-resistant GBM cells. Furthermore, HDAC6 inhibitors increase TMZ sensitivity and efficiently induce apoptosis in TMZ-resistant GBM cells. CONCLUSION: Selective inhibition of HDAC6 may be a promising strategy for the treatment of TMZ-resistant GBM.

MutL sliding clamps coordinate exonuclease-independent Escherichia coli mismatch repair.

A shared paradigm of mismatch repair (MMR) across biology depicts extensive exonuclease-driven strand-specific excision that begins at a distant single-stranded DNA (ssDNA) break and proceeds back past the mismatched nucleotides. Historical reconstitution studies concluded that Escherichia coli (Ec) MMR employed EcMutS, EcMutL, EcMutH, EcUvrD, EcSSB and one of four ssDNA exonucleases to accomplish excision. Recent single-molecule images demonstrated that EcMutS and EcMutL formed cascading sliding clamps on a mismatched DNA that together assisted EcMutH in introducing ssDNA breaks at distant newly replicated GATC sites. Here we visualize the complete strand-specific excision process and find that long-lived EcMutL sliding clamps capture EcUvrD helicase near the ssDNA break, significantly increasing its unwinding processivity. EcSSB modulates the EcMutL-EcUvrD unwinding dynamics, which is rarely accompanied by extensive ssDNA exonuclease digestion. Together these observations are consistent with an exonuclease-independent MMR strand excision mechanism that relies on EcMutL-EcUvrD helicase-driven displacement of ssDNA segments between adjacent EcMutH-GATC incisions.

Aldolase B impairs DNA mismatch repair and induces apoptosis in colon adenocarcinoma.

Evidence suggests that DNA repair capacity manifested by intact functional base excision repair and mismatch repair (MMR) pathways is related to the prognosis of multiple cancer types. Aldolase B (ALDOB) is well known for its role in metabolism and glycolysis. The expression of ALDOB in colon adenocarcinoma and the relationship between its expression and colon adenocarcinoma prognosis remain controversial; in addition, the potential role of ALDOB in DNA MMR has not yet been reported. In this study, we identified a cluster of DNA repair-related proteins that interact with ALDOB in the colon adenocarcinoma cell line HCT116. Expression analysis of colon adenocarcinoma data from the Cancer Genome Atlas (TCGA-COAD data, n = 551) indicated that ALDOB mRNA expression was significantly higher in specimens with microsatellite instability (MSI) than in specimens with microsatellite stability (MSS). Regarding prognosis, colon adenocarcinoma patients with high ALDOB mRNA expression had longer overall survival (OS). Higher expression of ALDOB protein was significantly correlated with MMR deficiency (d-MMR) in formalin-fixed paraffin-embedded (FFPE) patient specimens. The expression of ALDOB was significantly elevated in colon adenocarcinoma cell lines. Further evidence indicated that rather than affecting proliferation, ALDOB overexpression induced the functional loss of MMR proteins and in turn caused irreversible DNA damage via disrupting EZH2-Rad51 expression and then caused apoptosis by ERK inactivation. Overall, our study demonstrates that high ALDOB expression impairs DNA MMR and induces apoptosis in colon adenocarcinoma. ALDOB may be a new biomarker associated with d-MMR and an independent prognostic factor for colon adenocarcinoma.

Lynch syndrome-associated ultra-hypermutated pediatric glioblastoma mimicking a constitutional mismatch repair deficiency syndrome.

Pediatric glioblastoma multiforme (GBM) has a poor prognosis as a result of recurrence after treatment of surgery and radiochemotherapy. A small subset of pediatric GBMs presenting with an ultra-high tumor mutational burden (TMB) may be sensitive to immune checkpoint inhibition. Here we report a 16-yr-old male with an ultra-hypermutated GBM. After incomplete surgical resection, molecular analysis of the tumor identified unusually high numbers of mutations and intratumor heterogeneity by a hotspot next-generation sequencing (NGS) panel. Further comprehensive molecular profiling identified a TMB of 343 mutations/Mb. An ultra-hypermutation genotype in pediatric GBMs is suggestive of a constitutive mismatch repair deficiency syndrome (CMMRD), which often acquires additional somatic driver mutations in replicating DNA polymerase genes. Tumor sequencing identified two MSH6 nonsense variants, a hotspot POLE mutation and a mutational signature supportive of a germline MMR deficiency with a somatic POLE mutation. However, constitutional testing identified only one nonsense MSH6 variant consistent with a Lynch syndrome diagnosis. This case represents the first confirmed Lynch syndrome case mimicking CMMRD by manifesting as an ultra-hypermutated pediatric GBM, following somatic mutations in MSH6 and POLE These findings permitted the patient's enrollment in an anti-PD-1 clinical trial for children with ultra-hypermutated GBM. Immunotherapy response has resulted in the patient's stable condition for over more than 1 year postdiagnosis.

Mismatch Repair System Deficiency Is Associated With Response to Neoadjuvant Chemoradiation in Locally Advanced Rectal Cancer.

PURPOSE: Defective mismatch repair system (dMMR) has been shown to have a favorable impact on outcome in patients with colorectal cancer treated with surgery or immunotherapy, with adjuvant chemotherapy being discouraged unless there is nodal involvement. Its impact on radiosensitivity is unknown in patients with colorectal cancer. METHODS AND MATERIALS: Patients treated for locally advanced rectal cancer between 2000 and 2016 were studied. Reported points included age, sex, clinical and radiologic tumor stages at diagnosis, modalities of neoadjuvant treatment, posttreatment pathologic staging, tumor regression score, and local, distant relapse-free, and overall survival. An inverse probability of treatment weighting propensity score analysis was performed to evaluate the association of mismatch repair proficiency with surgical and clinical outcomes. RESULTS: Among the 296 patients included, 23 (7.8%) had dMMR. Median follow-up was 43.0 months (interquartile range, 27.9-66.7). Patients with dMMR were significantly younger than the others. After inverse probability of treatment weighting propensity score matching, dMMR patients had higher pathologic downstaging rate (P < .0001), higher tumor regression grade (P = .024), and a longer recurrence-free survival (P < .0001). CONCLUSIONS: dMRR was associated with significant tumor downstaging after neoadjuvant chemoradiation and with increased recurrence-free survival. dMMR patients may have more radiosensitive tumors.

Genetic and genomic basis of the mismatch repair system involved in Lynch syndrome.

Lynch syndrome is a cancer-predisposing syndrome inherited in an autosomal-dominant manner, wherein colon cancer and endometrial cancer develop frequently in the family, it results from a loss-of-function mutation in one of four different genes (MLH1, MSH2, MSH6, and PMS2) encoding mismatch repair proteins. Being located immediately upstream of the MSH2 gene, EPCAM abnormalities can affect MSH2 and cause Lynch syndrome. Mismatch repair proteins are involved in repairing of incorrect pairing (point mutations and deletion/insertion of simple repetitive sequences, so-called microsatellites) that can arise during DNA replication. MSH2 forms heterodimers with MSH6 or MSH3 (MutSα, MutSß, respectively) and is involved in mismatch-pair recognition and initiation of repair. MLH1 forms a complex with PMS2, and functions as an endonuclease. If the mismatch repair system is thoroughly working, genome integrity is maintained completely. Lynch syndrome is a state of mismatch repair deficiency due to a monoallelic abnormality of any mismatch repair genes. The phenotype indicating the mismatch repair deficiency can be frequently shown as a microsatellite instability in tumors. Children with germline biallelic mismatch repair gene abnormalities were reported to develop conditions such as gastrointestinal polyposis, colorectal cancer, brain cancer, leukemia, etc., and so on, demonstrating the need to respond with new concepts in genetic counseling. In promoting cancer genome medicine in a new era, such as by utilizing immune checkpoints, it is important to understand the genetic and genomic molecular background, including the status of mismatch repair deficiency.

Clear cell carcinoma of the endometrium: an immunohistochemical and molecular analysis of 45 cases.

The aim of the present paper is to study a cohort of pure selected endometrial clear cell carcinomas (ECCCs) from an immunohistochemical and molecular perspective to provide new data about the molecular profile of this disease. In detail, 45 consecutive patients with a proven diagnosis of pure ECCC, according to World Health Organization criteria, were included into the study. We determined the incidence of KRAS, BRAF, and PIK3CA mutations as well as the immunohistochemical expression of mismatch repair (MMR) proteins (MLH1, MSH2, MSH6, PMS2), estrogen, progesterone receptors, p16, and p53. Immunohistochemical analyses for α-methylacyl-coenzyme-A racemase and Napsin A were performed to support the diagnosis of ECC. All cases were positive for at least 1 of the 2 markers. In detail, 34 of 45 (75.5%) cases were positive for α-methylacyl-coenzyme-A racemase, and 40 of 45 (88.8%) cases showed positive staining for Napsin A. All selected cases exhibited negative immunostain for estrogen receptor and progesterone receptor, a "patchy" immunostain for p16, and a "wild-type" staining pattern for p53. Fifteen patients (15/45; 33.3%) showed loss of 1 or more MMR proteins by immunohistochemistry. Seven patients showed dual loss of MSH2 and MSH6, 4 patients (8.8%) showed isolated loss of MSH6, and the remaining 4 patients showed isolated loss of PMS2, respectively. Pyrosequencing analysis revealed the presence of 5 of 45 mutations (11%) at codon 12 in exon 2 of KRAS (3/5 p.G12D, 60%; 2/5 p. G12V, 40%) and 5 of 45 (11%) mutations in PIK3CA gene, of which 3 of 5 (60%) were in exon 9 of PIK3CA (2 p.E542K and 1 p.Q546K) and 2 of 5 (40%) were in exon 20 (p.H1047R). Two synchronous mutations affecting exon 9 of PIK3CA (p.Q546K) and exon 2, codon 12 of KRAS (p.G12D) were found. No mutations were detected in the hot spot region of BRAF. In conclusion, we provided detailed immunohistochemical and molecular data in a series of ECC, demonstrating a high incidence (33%) of MMR deficiencies detected by immunohistochemistry as well as a synchronous mutation affecting PIK3CA and KRAS genes. A more extensive interrogation of the genomic features of a much larger series of clear cell carcinomas will be required to define the genomic landscape of this subtype and to determine whether there are molecular alterations that are unique to, or significantly enriched in, clear cell tumors compared to other subtypes.