Emerging evidence supports the hypothesis that multicellular tumor clusters invade and seed metastasis. However, whether tumor-associated stroma induces epithelial–mesenchymal plasticity in tumor cell clusters, to promote invasion and metastasis, remains unknown. We demonstrate herein that carcinoma-associated fibroblasts (CAFs) frequently present in tumor stroma drive the formation of tumor cell clusters composed of two distinct cancer cell populations, one in a highly epithelial (E-cadherinhiZEB1lo/neg: Ehi) state and another in a hybrid epithelial/mesenchymal (E-cadherinloZEB1hi: E/M) state. The Ehi cells highly express oncogenic cell–cell adhesion molecules, such as carcinoembryonic antigen-related cell adhesion molecule 5 (CEACAM5) and CEACAM6 that associate with E-cadherin, resulting in increased tumor cell cluster formation and metastatic seeding. The E/M cells also retain associations with Ehi cells, which follow the E/M cells leading to collective invasion. CAF-produced stromal cell-derived factor 1 and transforming growth factor-β confer the Ehi and E/M states as well as invasive and metastatic traits via Src activation in apposed human breast tumor cells. Taken together, these findings indicate that invasive and metastatic tumor cell clusters are induced by CAFs via epithelial–mesenchymal plasticity.

Emerging evidence supports the theory that tumor cell clusters efficiently metastasize to distant organs. However, the roles of epithelial‐to‐mesenchymal transition (EMT) in metastasizing tumor cell clusters have not yet been fully elucidated. To investigate this issue, tumor fragments were dissected from 40 colorectal cancer (CRC) patients and implanted subcutaneously into immunodeficient mice. We observed that tumors developed from the tumor fragments obtained from 28 of the 40 CRC patients. The tumors were then dissociated into cell suspensions to be orthotopically injected into secondary mice. The tumors from 13 of the 28 patients progressed. Furthermore, metastases formed spontaneously in the liver and lungs from the tumor fragments obtained from 8 of these 13 patients. Moreover, employing a mathematical analysis, we showed that tumor cell clusters seeded these metastases significantly more often than did single tumor cells. Membrane E‐cadherin‐ and nuclear ZEB1‐positive tumor cells indicating the hybrid epithelial/mesenchymal state were also detected in primary tumors of various CRC patients, and in the corresponding patient‐derived xenografts (PDXs) and circulating tumor cell clusters in the bloodstreams of mice. In contrast, ZEB1 staining was barely detectable in the patient‐matched liver metastases presumably developing through mesenchymal‐to‐epithelial transition. Inhibition of E‐cadherin or ZEB1 expression by shRNA notably prevented the PDX‐derived tumor organoids from colonizing the liver, when injected intrasplenically into mice, indicating E‐cadherin and ZEB1 expressions to be required for their metastatic colonization. Taken together, these findings suggest that the epithelial/mesenchymal state mediates metastatic seeding of human CRC cell clusters into distant organs.

The frequency of microsatellite instability (MSI) is reportedly extremely low in breast cancer, despite widespread clinical expectations that many patients would be responsive to immune‐checkpoint inhibitors (ICI). Considering that some triple‐negative breast cancers (TNBC) responded well to ICI in a clinical trial and that a high density of tumor‐infiltrating lymphocytes (TILs) is frequently observed in other cancers with high levels of microsatellite instability (MSI‐H), we hypothesized that some TNBC with a high density of TILs would be MSI‐H. Medullary carcinoma (MedCa) of the breast, a rare histological type, is characterized by a high density of TILs. Considering that MedCa of the colon is often MSI‐H, we suspected that MedCa in breast cancer might also include MSI‐H tumors. Therefore, we conducted MSI tests on such breast cancers with a high density of TILs. The MSI status of 63 TIL‐high TNBC and 38 MedCa tumors, all from Asian women who had undergone curative surgery, were determined retrospectively. DNA mismatch repair (MMR) proteins and PD‐L1 expression were also investigated immunohistochemically. All samples were microsatellite stable, being negative for all microsatellite markers. TIL‐high TNBC with low MLH1 protein had higher levels of PD‐L1 in stromal immune cells ( P = .041). MedCa tumors showed significantly higher PD‐L1 expression in immune cells than in TIL‐high TNBC (<.001). We found that MSI‐H tumors were absent in TIL‐high breast cancers. Examination of MMR proteins, not a purpose of Lynch syndrome screening, may merit further studies to yield predictive information for identifying patients who are likely to benefit from ICI.

A 15-year-old boy presented with an anaplastic supratentorial ependymoma causing massive intratumoral calcification, without contributory medical and family history, and manifesting as persistent headache for 2 months. Physical examination found no neurological deficit except for visual defect in the right lower quadrant, with intact visual acuity. Blood examination showed no abnormalities. Cranial computed tomography revealed a huge calcified mass in the left parietooccipital lobe, with extensive perilesional brain edema. Cranial radiography showed diffuse and symmetrical thinning of the calvarial bone. Magnetic resonance imaging confirmed the tumor as an assembly of medullated masses with extraventricular location, 7 × 6.5 × 6.5 cm in diameter, and appearing as heterogeneous intensity on both T 1 -and T 2 -weighted images with inhomogeneous enhancement except for the central cores. The patient underwent tumor resection. Intraoperative findings revealed that the cortical veins overlying the tumor were reddish and moderately engorged. The hypervascular tumor, entirely extraventricular in location, was totally resected without neurological deterioration. Histological examination revealed that the tumor was highly cellular with hyperchromatic nuclei and cell atypia. Necrosis, mitotic figures, and perivascular pseudorosette formations were frequently seen. Immunohistochemical study showed positive staining for glial fibrillary acidic protein, S-100 protein, vimentin, and epithelial membrane antigen, but negative for synaptophysin. The MIB-1 labeling index was 26.5%. The findings were compatible with anaplastic ependymoma (World Health Organization classification grade 3). Ependymoma should be included in the differential diagnosis of a supratentorially located, extraventricular mass with massive intratumoral calcification.

To prevent aggressive surgery it is important to recognize that this tumor is a benign and unusual appearing variant of leiomyoma. A fertility-sparing surgical procedure should be considered if the patient wishes to preserve her fertility.

Children born to women who experience stress during pregnancy have an increased risk of cancer in later life, but no previous animal studies have tested such a link. We questioned whether prenatal stress (PS) in A/J mice affected the development of lung tumors after postnatal response to tobacco-specific nitrosamine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). Timed-bred A/J mice were randomly assigned on gestation day 12.5 to PS by restraint for 5 consecutive days or control (no restraint). Adult offspring of control and stressed pregnancies were all treated with three NNK injections (50 mg/kg every other day) and euthanized 16 weeks later to examine their lungs. Compared with controls, PS dams exhibited significantly increased levels of plasma corticosterone, increased adrenal weights and decreased fetus weights without fetal loss. Prenatally stressed litters had a significantly higher neonatal death rate within first week of life, and surviving male and female offspring developed lung epithelial proliferations with increase multiplicity, increased area and aggressive morphology. PS also induced more advanced atypical adenomatous hyperplasia lesions. We found no difference in lung NNK-derived methyl DNA adducts, but PS did significantly enhance CD3+ T cell and Foxp3+ T cell tumor infiltration. PS significantly increases multiplicity, area of NNK-induced lung tumors and advanced morphology. PS did not affect production of NNK-derived methyl DNA adducts but did increase lymphocytic infiltration of lung tumors. To our knowledge, this is the first animal model of PS with evaluation of cancer development in offspring.

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Aim Microsatellite instability (MSI), which reflects loss of DNA mismatch repair (MMR) activity, and immunohistochemistry (IHC) for MMR proteins are employed as screening examinations for Lynch syndrome (LS). Recent studies revealed that there is a population of MSI‐high tumors in sporadic endometrial cancer (EC). However, MSI data for Japanese EC patients are scarce. Furthermore, sporadic estrogen‐dependent EC (type I) is generally considered to arise from hyperplasia. Because LS is usually associated with type I EC, we hypothesized that MSI might be involved in the oncogenic process in some sporadic EC. We conducted MSI testing to reveal MSI status in sporadic Japanese EC. IHC for MMR proteins was also performed. Methods Ninety‐eight tissue samples of sporadic ECs from Japanese patients were used for IHC and MSI examinations. We also evaluated MMR protein expressions in the background normal endometrium. Results Microsatellite instability‐high was observed in 10.2% of 98 cases with sporadic EC, a lower percentage than that in Western studies. Loss of some MMR proteins was observed in 23 cases (23.5%) and there was a significant correlation with MSI‐high status (P < 0.001). Concerning the background endometrium, two cases showed partial loss of MLH1 and PMS2, corresponding to adjacent EC lesions, suggesting that MMR deficiency may already be present in the background endometrium. Conclusion The MSI‐high rate was low in our Japanese cohort. Our data confirmed the usefulness of MMR protein assessment for MSI screening in Japanese EC patients. Furthermore, IHC of the background endometrium might reveal the mechanism of MSI‐high tumorigenesis.