A rare case of intrahepatic cholangiocarcinoma with tumor thrombus in the bile duct.

Intrahepatic cholangiocarcinoma (ICC) is a refractory liver malignancy; however, as its histological characteristics have been clarified, a good operative strategy for the subtypes of ICC can be expected. A 72-year-old woman was diagnosed with a large primary liver cancer with biliary tumor thrombus (BTT) and obstructive jaundice. An enhanced imaging modality showed hypervascular ICC or combined hepatocellular carcinoma (HCC). As her liver functional parameters permitted major hepatectomy, preoperative biliary drainage was performed, followed by a radical left hepatectomy accompanied by tumor thrombectomy with D2 lymphadenectomy. During the operation, the BTT was found to have widely spread into the right hepatic duct and the common bile duct and was histologically diagnosed as an adenocarcinoma. As ductal cancer invasion was not macroscopically observed, the planned operation was completed. The postoperative histological diagnosis was determined by discussion to be a rare mass-forming ICC with BTT. Her postoperative course was uneventful, and a 1-year survival without tumor relapse was observed with adjuvant chemotherapy. In the field of biliary surgery, although advanced ICC still has a poor prognosis, curable surgical intervention is possible for specific findings, such as BTT and HCC with BTT.

FBXW7 is involved in the acquisition of the malignant phenotype in epithelial ovarian tumors.

FBXW7 is a ubiquitin ligase that mediates ubiquitylation of oncoproteins, such as c-Myc, cyclin E, Notch and c-Jun. FBXW7 is a known tumor-suppressor gene, and mutations in FBXW7 have been reported in various human malignancies. In this study, we examined the sequences of the FBXW7 and p53 genes in 57 ovarian cancer clinical samples. Interestingly, we found no FBXW7 mutations associated with amino acid changes. We also investigated FBXW7 expression levels in 126 epithelial ovarian tumors. FBXW7 expression was negatively correlated with the malignant potential of ovarian tumors. That is to say, FBXW7 expression levels in ovarian cancer samples were significantly lower than those in borderline and benign tumors (P < 0.01). FBXW7 expression levels in serous carcinoma samples were the lowest among four major histological subtypes. In addition, p53-mutated ovarian cancer samples showed significantly lower levels of FBXW7 expression compared with p53 wild-type cancer samples (P < 0.001). DNA methylation arrays and bisulfite PCR sequencing experiments revealed that 5'-upstream regions of FBXW7 gene in p53-mutated samples were significantly higher methylated compared with those in p53 wild-type samples (P < 0.01). This data indicates that p53 mutations might suppress FBXW7 expression through DNA hypermethylation of FBXW7 5'-upstream regions. Thus, FBXW7 expression was downregulated in ovarian cancers, and was associated with p53 mutations and the DNA methylation status of the 5'-upstream regions of FBXW7.

Novel Nonsense Mutation in the NLRP7 Gene Associated with Recurrent Hydatidiform Mole.

AIM: This study aimed to clarify the genetic and epigenetic features of recurrent hydatidiform mole (RHM) in Japanese patients. METHODS: Four Japanese isolated RHM cases were analyzed using whole-exome sequencing. Villi from RHMs were collected by laser microdissection for genotyping and DNA methylation assay of differentially methylated regions (DMRs). Single nucleotide polymorphisms of PEG3 and H19 DMRs were used to confirm the parental origin of the variants. RESULTS: A novel homozygous nonsense mutation in NLRP7 (c.584G>A; p.W195X) was identified in 1 patient. Genotyping of one of her molar tissue revealed that it was biparental but not androgenetic in origin. Despite the fact that the RHM is biparental, maternally methylated DMRs of PEG3, SNRPN and PEG10 showed complete loss of DNA methylation. A paternally methylated DMR of H19 retained normal methylation. CONCLUSIONS: This is the first Japanese case of RHM with a novel homozygous nonsense NLRP7 mutation and a specific loss of maternal DNA methylation of DMRs. Notably, the mutation was identified in an isolated case of an ethnic background that has not previously been studied in this context. Our data underscore the involvement of NLRP7 in RHM pathophysiology and confirm that DNA methylation of specific regions is critical.

Identification of the Critical Site of Calponin 1 for Suppression of Ovarian Cancer Properties.

BACKGROUND: Although several studies have demonstrated the tumor suppressive function of CNN1 (calponin 1), no studies have performed a site-specific analysis of CNN1 on tumor cell activities. MATERIALS AND METHODS: We herein studied the site-specific effects of CNN1 in ovarian cancer cells using full-length CNN1 (fCNN1), three CNN1 repeats (3CNRs), or the first CNN1 repeat (CNR1) expression vectors. Ovarian cancer cells stably expressing each construct were analyzed for in vitro proliferation, cell motility, invasion, and soft agar assays. An in vitro model of pleural dissemination was also established. RESULTS: Cell proliferation, anchorage-independent colony formation, cell motility, and cell invasion were all suppressed in fCNN1, 3CNRs, and CNR1-stably-expressing cells. CNN1 expression in mesothelial cells suppressed cancer cell invasion into a monolayer of mesothelial cells. CONCLUSION: CNR1 showed similar suppressive effects as fCNN1. Results suggest CNR1 as a potential small synthetic peptide candidate for therapeutic strategies against ovarian cancer.

Regulation of the Mechanism of TWIST1 Transcription by BHLHE40 and BHLHE41 in Cancer Cells.

BHLHE40 and BHLHE41 (BHLHE40/41) are basic helix-loop-helix type transcription factors that play key roles in multiple cell behaviors. BHLHE40/41 were recently shown to be involved in an epithelial-to-mesenchymal transition (EMT). However, the precise mechanism of EMT control by BHLHE40/41 remains unclear. In the present study, we demonstrated that BHLHE40/41 expression was controlled in a pathological stage-dependent manner in human endometrial cancer (HEC). Our in vitro assays showed that BHLHE40/41 suppressed tumor cell invasion. BHLHE40/41 also suppressed the transcription of the EMT effectors SNAI1, SNAI2, and TWIST1. We identified the critical promoter regions of TWIST1 for its basal transcriptional activity. We elucidated that the transcription factor SP1 was involved in the basal transcriptional activity of TWIST1 and that BHLHE40/41 competed with SP1 for DNA binding to regulate gene transcription. This study is the first to report the detailed functions of BHLHE40 and BHLHE41 in the suppression of EMT effectors in vitro. Our results suggest that BHLHE40/41 suppress tumor cell invasion by inhibiting EMT in tumor cells. We propose that BHLHE40/41 are promising markers to predict the aggressiveness of each HEC case and that molecular targeting strategies involving BHLHE40/41 and SP1 may effectively regulate HEC progression.

SNP55, a new functional polymorphism of MDM2-P2 promoter, contributes to allele-specific expression of MDM2 in endometrial cancers.

BACKGROUND: The functional single nucleotide polymorphism (SNP) in the MDM2 promoter region, SNP309, is known to be associated with various diseases, particularly cancer. Although many studies have been performed to demonstrate the mechanism of allele-specific expression (ASE) on SNP309, they have only utilized in vitro techniques. It is unknown whether ASE of MDM2 is ascribed solely to SNP309, in vivo. METHODS: We attempted to evaluate ASE of MDM2 in vivo using post-labeling followed by automated capillary electrophoresis under single-strand conformation polymorphism conditions. For measuring a quantitative difference, we utilized the SNPs on the exons of MDM2 as markers, the status of which was heterozygous in a large population. To address the cause of ASE beyond 20%, we confirmed sequences of both MDM2-3'UTR and promoter regions. We assessed the SNP which might be the cause of ASE using biomolecular interaction analysis and luciferase assay. RESULTS: ASE beyond 20% was detected in endometrial cancers, but not in cancer-free endometria samples only when an SNP rs1690916 was used as a marker. We suspected that this ASE in endometrial cancer was caused by the sequence heterogeneity in the MDM2-P2 promoter, and found a new functional polymorphism, which we labelled SNP55. There was no difference between cancer-free endometria and endometrial cancer samples neither for SNP55 genotype frequencies nor allele frequencies, and so, SNP55 alone does not affect endometrial cancer risk. The SNP55 status affected the DNA binding affinity of transcription factor Sp1 and nuclear factor kappa-B (NFκB). Transcriptional activity of the P2 promoter containing SNP55C was suppressed by NFκB p50 homodimers, but that of SNP55T was not. Only ASE-positive endometrial cancer samples displayed nuclear localization of NFκB p50. CONCLUSIONS: Our findings suggest that both the SNP55 status and the NFκB p50 activity are important in the transcriptional regulation of MDM2 in endometrial cancers.

Genomic, Epigenomic, and Transcriptomic Profiling towards Identifying Omics Features and Specific Biomarkers That Distinguish Uterine Leiomyosarcoma and Leiomyoma at Molecular Levels.

Uterine leiomyosarcoma (LMS) is the worst malignancy among the gynecologic cancers. Uterine leiomyoma (LM), a benign tumor of myometrial origin, is the most common among women of childbearing age. Because of their similar symptoms, it is difficult to preoperatively distinguish the two conditions only by ultrasound and pelvic MRI. While histopathological diagnosis is currently the main approach used to distinguish them postoperatively, unusual histologic variants of LM tend to be misdiagnosed as LMS. Therefore, development of molecular diagnosis as an alternative or confirmatory means will help to diagnose LMS more accurately. We adopted omics-based technologies to identify genome-wide features to distinguish LMS from LM and revealed that copy number, gene expression, and DNA methylation profiles successfully distinguished these tumors. LMS was found to possess features typically observed in malignant solid tumors, such as extensive chromosomal abnormalities, overexpression of cell cycle-related genes, hypomethylation spreading through large genomic regions, and frequent hypermethylation at the polycomb group target genes and protocadherin genes. We also identified candidate expression and DNA methylation markers, which will facilitate establishing postoperative molecular diagnostic tests based on conventional quantitative assays. Our results demonstrate the feasibility of establishing such tests and the possibility of developing preoperative and noninvasive methods.

Genome-wide parent-of-origin DNA methylation analysis reveals the intricacies of human imprinting and suggests a germline methylation-independent mechanism of establishment.

Differential methylation between the two alleles of a gene has been observed in imprinted regions, where the methylation of one allele occurs on a parent-of-origin basis, the inactive X-chromosome in females, and at those loci whose methylation is driven by genetic variants. We have extensively characterized imprinted methylation in a substantial range of normal human tissues, reciprocal genome-wide uniparental disomies, and hydatidiform moles, using a combination of whole-genome bisulfite sequencing and high-density methylation microarrays. This approach allowed us to define methylation profiles at known imprinted domains at base-pair resolution, as well as to identify 21 novel loci harboring parent-of-origin methylation, 15 of which are restricted to the placenta. We observe that the extent of imprinted differentially methylated regions (DMRs) is extremely similar between tissues, with the exception of the placenta. This extra-embryonic tissue often adopts a different methylation profile compared to somatic tissues. Further, we profiled all imprinted DMRs in sperm and embryonic stem cells derived from parthenogenetically activated oocytes, individual blastomeres, and blastocysts, in order to identify primary DMRs and reveal the extent of reprogramming during preimplantation development. Intriguingly, we find that in contrast to ubiquitous imprints, the majority of placenta-specific imprinted DMRs are unmethylated in sperm and all human embryonic stem cells. Therefore, placental-specific imprinting provides evidence for an inheritable epigenetic state that is independent of DNA methylation and the existence of a novel imprinting mechanism at these loci.

A definitive haplotype map of structural variations determined by microarray analysis of duplicated haploid genomes.

Complete hydatidiform moles (CHMs) are tissues carrying duplicated haploid genomes derived from single sperms, and detecting copy number variations (CNVs) in CHMs is assumed to be sensitive and straightforward methods. We genotyped 108 CHM genomes using Affymetrix SNP 6.0 (GEO#: GSE18642) and Illumina 1 M-duo (GEO#: GSE54948). After quality control, we obtained 84 definitive haplotype consisting of 1.7 million SNPs and 2339 CNV regions. The results are presented in the database of our web site (http://orca.gen.kyushu-u.ac.jp/cgi-bin/gbrowse/humanBuild37D4_1/).

Establishment of a new diagnostic method for hydropic villi by using TSSC3 antibody.

A total of 297 samples of hydropic villi were classified according to DNA polymorphisms as androgenetic moles, dispermic triploids, or biparental diploids. A subset of 267 appropriate samples was included in the study. Most of the macroscopically diagnosed complete mole cases were genetically androgenetic in origin. The partial mole cases consisted of 30 androgenetic moles and 12 dispermic triploids. For the 59 cases macroscopically categorized as hydropic abortion, the genetic analysis revealed 38 androgenetic moles, seven dispermic triploids and 14 biparental diploids. These results showed that a new diagnostic method was required for the management of patients with hydropic villi. We identified the TSSC imprint gene of which expression was shown in normal and partial mole villi but was silenced in complete mole villi. Immunohistochemistry using the TSSC3 antibody demonstrated its efficacy as the differential diagnostic method. TSSC3 play an important role in the differentiation from trophoblast stem cells to progenitors and/or labyrinth trophoblast through the TSSC3/PI3K/Akt/Mash2 signaling pathway.

Doppler sonographic evaluation of arteriovenous shunt flow in a fetus with dural sinus malformation.

Dural sinus malformation (DSM) is a rare congenital malformation characterized by a dilated dural sinus pouch. We present a case of prenatally diagnosed DSM and propose a parameter to predict poor fetal outcome. Detailed ultrasonography at 26 weeks of our patient showed an intracranial cyst in the left posterior fossa. Color Doppler study indicated an arteriovenous shunt within the cyst with increased blood flow velocity. Based on these findings, fetal DSM with arteriovenous shunt was diagnosed. Because of fetal hydrops with high-output cardiac failure and maternal pregnancy-induced hypertension, labor was induced at 32 weeks and resulted in stillbirth. In conclusion, based on the present case, we can deduce that color Doppler study is useful for prenatal diagnosis of DSM with arteriovenous shunt and that a high-flow velocity to the cystic lesion is a possible predictor of hydropic change in such fetuses.

Association of MDM2 SNP309 and TP53 Arg72Pro polymorphisms with risk of endometrial cancer.

The incidence of endometrial cancer, a common gynecological malignancy, is increasing in Japan. We have previously shown that the ER/MDM2/p53/p21 pathway plays an important role in endometrial carcinogenesis. In the present study, we investigated the effects of germline single nucleotide polymorphisms in murine double minute 2 (MDM2) SNP309, TP53 Arg72Pro, ESR1 PvuII and XbaI, and p21 codon 31 on endometrial cancer risk. We evaluated these polymorphisms in DNA samples from 125 endometrial cancer cases and 200 controls using polymerase chain reaction-based restriction fragment length polymorphism. The association of each genetic polymorphism with endometrial cancer was examined by the odds ratio and 95% confidence interval, which were obtained using logistic regression analysis. The SNP309 GG genotype non-significantly increased the risk of endometrial cancer. The 95% confidence interval for the GG genotype vs. the TT genotype of MDM2 SNP309 was 1.76 (0.93-3.30). Endometrial cancer was not associated with tested SNP genotypes for TP53, ESR1 and p21. The combination of SNP309 GG + TG and TP53 codon 72 Arg/Arg significantly increased endometrial cancer risk. The adjusted OR was 2.53 (95% confidence interval, 1.03-6.21) and P for the interaction was 0.04. This result was supported by in vitro data showing that endometrial cancer cell lines with the SNP309 G allele failed to show growth inhibition by treatment with RITA, which reduces p53-MDM2 binding. The presence of the SNP309 G allele and TP53 codon 72 Arg/Arg genotype is associated with an increased risk of endometrial cancer in Japanese women.

Well-differentiated villoglandular adenocarcinoma of the uterine cervix: assessment of cytological features by histological subtypes.

OBJECTIVE: Well-differentiated villoglandular adenocarcinoma (VGA) of the cervix involves papillae lined by different types of epithelial cells that are histologically subclassified into endocervical, endometrioid, or intestinal subtypes. The objective of the current study was to evaluate the definite cytological features of VGA by histological subtype. STUDY DESIGN: We examined 8 cervical smears from patients confirmed to have pure VGA and classified them into the 3 histological subtypes. RESULTS: The cervical smears were highly cellular and had a relatively clean background. The nuclei had minimal anisonucleosis and fine granular chromatin with almost inconspicuous nucleoli. The characteristic findings of the endocervical type were a palisading arrangement consisting of columnar or spindle-shaped cells with apical or elongated nuclei. Small but clear nucleoli were identified only in the endocervical type. In the endometrioid type, tumor cells consisted of cohesive sheets with smooth edges and very round nuclei. Cytoplasmic vacuolation was never observed in the endometrioid type. The tumor cells in the intestinal type were prominent with abundant cytoplasmic mucin. CONCLUSIONS: We demonstrated that the cytological features of this tumor can vary depending on the histological subtype and one should be aware of these features in order to improve diagnostic accuracy.

The maternally expressed gene Tssc3 regulates the expression of MASH2 transcription factor in mouse trophoblast stem cells through the AKT-Sp1 signaling pathway.

Tssc3 is a maternally expressed/paternally silenced imprinted gene. Recent evidence suggests that the loss of TSSC3 results in placental overgrowth in mice. These findings showed that the TSSC3 gene functions as a negative regulator of placental growth. In this study, we describe the function of TSSC3 and its signaling pathway in mouse trophoblast stem (TS) cell differentiation. First of all, we tested Tssc3 expression levels in TS cells. TS cells expressed Tssc3, and its expression level was the highest from day 1 to 4 but was down-regulated at day 5 after the induction of differentiation. Overexpression of TSSC3 in TS cells up-regulated Gcm1 and Mash2, which are marker genes of mouse trophoblast differentiation. Down-regulation of TSSC3 by siRNA enhanced Pl1 and Tpbpa expression in TS cells cultured under stem cell conditions, suggesting the contribution of TSSC3 to the differentiation from TS to trophoblast progenitors and/or labyrinth trophoblasts. TSSC3 activated the PI3K/AKT pathway through binding with phosphatidylinositol phosphate lipids and enhanced the activity of a promoter containing an E-box structure, which is the binding sequence of the Mash2 downstream target gene promoter. PI3K inhibitor suppressed the promoter activity induced by TSSC3. TSSC3 induced Sp1 translocation from cytoplasm to nucleus through the PI3K/AKT pathway. Nuclear Sp1 activated the Mash2 transcription by Sp1 binding with a consensus Sp1-binding motif. This is the first report describing that TSSC3 plays an important role in the differentiation from TS to trophoblast progenitors and/or labyrinth trophoblasts through the TSSC3/PI3K/AKT/MASH2 signaling pathway.

"Piling up" clear cells in müllerian-type mucinous and mixed cell-type borderline tumor do not represent concomitant clear cell neoplasms.

The nature of "piling up" proliferation of clear cells in müllerian mucinous/mixed borderline tumor has not been well characterized. The purpose of this study was to clarify whether or not such clear cells represent concomitant clear cell neoplasms. First, we carefully reviewed hematoxylin and eosin slides taken from 139 ovarian tumors diagnosed as clear cell carcinoma (112 cases) and müllerian mucinous/mixed borderline tumor (27 cases) to clarify (1) the frequency of piling-up clear cells in müllerian mucinous/mixed borderline tumor and (2) the frequency of the coexistence of typical clear cell carcinoma and müllerian mucinous/mixed borderline tumor. Second, we investigated the immunohistochemical expression of estrogen receptor, hepatocyte nuclear factor-1ß, and glypican-3 in proliferating clear cells in both tumors. We identified piling-up clear cells in 56% of müllerian mucinous/mixed borderline tumors. Such clear cells lacked the severe nuclear atypia, complex branching, and dense hyalinized cores of typical clear cell carcinoma. We did not find coexistence of typical clear cell carcinoma and müllerian mucinous/mixed borderline tumor in any tumors. Piling-up clear cells and endocervical-like mucinous cells were positive for estrogen receptor but negative for hepatocyte nuclear factor-1ß and glypican-3. Most clear cell carcinomas showed a hepatocyte nuclear factor-1ß-positive/estrogen receptor-negative immunophenotype, and about half of them were glypican-3 positive. In conclusion, piling-up clear cells in müllerian mucinous/mixed borderline tumor do not represent concomitant clear cell neoplasms because clear cell carcinoma and müllerian mucinous/mixed borderline tumor hardly ever coexist and because such clear cells in both tumors are immunophenotypically distinct.

Antenatally diagnosed congenital orbital teratoma in which rupture was associated with intrauterine fetal death.

We report a case of a fetus with a congenital orbital teratoma (COT), in which rupture of the tumor was associated with an intrauterine fetal demise. An ultrasound scan at 27 weeks' revealed a solid and cystic, complex mass in the orbital region with extensive vascularization suggestive of an orbital cystic teratoma. Magnetic resonance imaging (MRI) supported this diagnosis and clarified tumor localization. At 32 weeks', the patient presented with fetal demise and rupture of the mass was noted. Fetal COTs, like sacrococcygeal teratomas, carry the risk of rupture. MRI in utero is useful for evaluating the extent of disease.

Significance of pelvic magnetic resonance imaging in preoperative diagnosis of incarcerated retroverted gravid uterus with a large anterior leiomyoma: a case report.

BACKGROUND: Incarceration of the gravid uterus is a rare but serious complication of pregnancy. The often required cesarean section is technically complicated, and preoperative planning is critical. An important initial surgical step is to lift the fundus out of the pelvis prior to creating the hysterotomy in order to facilitate adequate visualization of the pelvic anatomy. CASE: A 38-year-old primigravida with uterine incarceration from a large anterior leiomyoma underwent cesarean delivery at 29 weeks' gestation. In this case, a failure of the fundal height to increase was not appreciated as the anterior leiomyoma was palpated to represent the fundus. Intraoperatively the uterus was unable to be repositioned because of the leiomyoma. However, the surgery did proceed smoothly primarily due to the highly detailed images obtained on pelvic magnetic resonance imaging. CONCLUSION: Although uterine incarceration is rare, knowledge of this condition is important. Magnetic resonance imaging is a useful tool in that it enables the detailed evaluation of the pelvic anatomy in cases with suspected uterine incarceration.

E-cadherin nuclear staining is useful for the diagnosis of ovarian adult granulosa cell tumor.

We recently have demonstrated nuclear localization of E-cadherin in ovarian adult granulosa cell tumors (Histopathology 2011;58:423). The purpose of the present study is to investigate the diagnostic utility of E-cadherin nuclear staining for the differential diagnosis between ovarian adult granulosa cell tumor and its morphological mimics. Tissue samples taken from 81 ovarian tumors and 20 extraovarian tumors were immunohistochemically stained using monoclonal anti-E-cadherin antibody recognizing cytoplasmic domain (clone 36 supplied by BD Biosciences, San Jose, CA). The ovarian tumors consisted of 30 adult granulosa cell tumors, 3 Sertoli-stromal cell tumors, 14 fibrothecomas, 5 carcinoid tumors, 1 large cell neuroendocrine carcinoma, 18 endometrioid adenocarcinomas, and 10 poorly differentiated serous adenocarcinomas. Extraovarian tumors consisted of 16 uterine endometrial stromal neoplasms and 4 pulmonary small cell carcinomas. Only tumor cells with nuclear staining were considered positive in this study. Ninety percent of adult granulosa cell tumors, 67% of Sertoli-stromal cell tumors, 64% of fibrothecomas, 75% of endometrial stromal neoplasms, 75% of small cell carcinomas, and the one large cell neuroendocrine carcinoma showed E-cadherin nuclear expression, whereas all the ovarian carcinoid tumors, endometrioid adenocarcinomas, and poorly differentiated serous adenocarcinomas were negative. E-cadherin nuclear staining is useful in distinguishing between adult granulosa cell tumors and ovarian adenocarcinomas or carcinoid tumors. However, it is of limited use for distinguishing between adult granulosa cell tumors and endometrial stromal neoplasms or small cell carcinomas. E-cadherin should be included in the immunohistochemical panel for an accurate diagnosis of ovarian adult granulosa cell tumors.

Sodium butyrate inhibits the self-renewal capacity of endometrial tumor side-population cells by inducing a DNA damage response.

We previously isolated side-population (SP) cells from a human endometrial cancer cell line, Hec1, and determined that Hec1-SP cells have cancer stem-like cell features. In this study, we isolated SP cells and non-SP (NSP) cells derived from a rat endometrial cell line expressing human [(12)Val] KRAS (RK12V cells) and determined the SP phenotype. RK12V-SP cells showed self-renewal capacity, the potential to develop into stromal cells, reduced expression levels of differentiation markers, long-term proliferating capacity in cultures, and enhanced tumorigenicity, indicating that RK12V-SP cells have cancer stem-like cell features. RK12V-SP cells also display higher resistance to conventional chemotherapeutic drugs. In contrast, treatment with a histone deacetylases (HDAC) inhibitor, sodium butyrate (NaB), reduced self-renewal capacity and completely suppressed colony formation of RK12V-SP cells in a soft agar. The levels of intracellular reactive oxygen species (ROS) and the number of γH2AX foci were increased by NaB treatment of both RK12V-SP cells and RK12V-NSP cells. The expression levels of γH2AX, p21, p27, and phospho-p38 mitogen-activated protein kinase were enhanced in RK12V-SP cells compared with RK12V-NSP cells. These results imply that treatment with NaB induced production of intracellular ROS and DNA damage in both RK12V-SP and RK12V-NSP cells. Following NaB treatment, DNA damage response signals were enhanced more in RK12V-SP cells than in RK12V-NSP cells. This is the first article on an inhibitory effect of NaB on proliferation of endometrial cancer stem-like cells. HDAC inhibitors may represent an attractive antitumor therapy based upon their inhibitory effects on cancer stem-like cells.