Kei Kushitani

Ancillary assays, including BAP1 (BRCA‐1‐associated protein 1), MTAP (methylthioadenosine phosphorylase), and Merlin immunohistochemistry (IHC), are effective in discriminating pleural mesothelioma (PM) from reactive mesothelial proliferations (RMP). IHC of Merlin, a protein product of the neurofibromin 2 gene, was most recently developed. Our previous study suggested uneven occurrence of Merlin loss within PM tissues. This was further investigated here in a total of 41 tissues of PM obtained from seven institutions. Partial or diffuse Merlin loss was detected with excellent interobserver agreement (kappa: 0.82). Of the 34 PM cases with interobserver consensus, partial and diffuse loss of Merlin expression were each observed in 13 cases (38%). PM with partial Merlin loss exhibited either discrete or intermingled spatial distribution of Merlin‐lost cells. BAP1 or MTAP showed partial loss in none or only 5% of PM cases, respectively. The diagnostic sensitivity for PM was enhanced to 91% with addition of diffuse and partial Merlin loss to a combination of BAP1 and MTAP loss while maintaining 100% specificity. Although detection of Merlin loss as well as BAP1 and MTAP losses is effective for distinguishing PM from RMP, pathologists should be familiar with partial Merlin loss when interpreting Merlin IHC results.

The differential diagnosis of epithelioid mesothelioma and reactive mesothelial hyperplasia can be challenging based on morphology alone, particularly in small specimens. Consequently, the use of ancillary techniques, such as immunohistochemistry for BRCA1‐associated protein 1, methylthioadenosine phosphorylase, and CDKN2A/p16 fluorescence in situ hybridization, has been considered a reliable method. Moreover, the potential of Merlin, enhancer of zeste homolog 2, 5‐hydroxymethylcytosine, and c‐Met immunohistochemistry in differential diagnosis has been reported. We conducted BRCA1‐associated protein 1, methylthioadenosine phosphorylase, Merlin, enhancer of zeste homolog 2, 5‐hydroxymethylcytosine, and c‐Met immunohistochemistry in 43 epithelioid mesothelioma and 28 reactive mesothelial hyperplasia samples. BRCA1‐associated protein 1 and/or methylthioadenosine phosphorylase achieved the highest sensitivity (83.7%), while the addition of Merlin improved the sensitivity to 86.0% while maintaining 100% specificity. We confirmed that the addition of Merlin to BRCA1‐associated protein 1 and methylthioadenosine phosphorylase improved the sensitivity in the differential diagnosis of epithelioid mesothelioma and reactive mesothelial hyperplasia while maintaining 100% specificity. Moreover, the utilization of enhancer of zeste homolog 2, 5‐hydroxymethylcytosine, and c‐Met cannot be unequivocally endorsed, as these markers have not demonstrated 100% specificity, despite their capacity to modestly enhance sensitivity when employed in conjunction with BRCA1‐associated protein 1 and methylthioadenosine phosphorylase.

Introduction: There have been only a few cases showing the efficacy of pembrolizumab on granulocyte-colony-stimulating factor (G-CSF)-producing non-small-cell lung cancer (NSCLC) with high programmed cell death ligand 1 (PD-L1) expression. Herein, we report the first case showing the efficacy of pembrolizumab for G-CSF-producing NSCLC with high PD-L1 expression, although the patient had factors indicative of poor pembrolizumab efficacy, such as poor performance status (PS) due to the tumor-induced inflammation and corticosteroids administration. Case Presentation: A 77-year-old woman was diagnosed with G-CSF-producing NSCLC-not otherwise specified, classified as clinical stage IVB, T2N3M1c. She had fever and her PS was 3, and her C-reactive protein (CRP) was 6.47 mg/dL due to inflammation by a G-CSF-producing tumor. Thus, we initiated the administration of dexamethasone (3.3 mg/day). Her fever abated the next day, and CRP dropped to 3.22 mg/dL after 4 days. Driver mutations were negative, and PD-L1, tumor proportion score, was highly expressed at 100%. Thus, pembrolizumab was started. Subsequently, the white blood cell count decreased, and the tumor shrank, indicating a partial response. After three cycles of pembrolizumab therapy, the anorexia improved, and she was discharged. The patient developed sclerosing cholangitis after discharge. Therefore, the pembrolizumab treatment was discontinued. The primary lesion was enlarged, indicating progressive disease. However, the patient and her family did not want additional treatment. Finally, her progression-free survival and overall survival were 6 and 7 months, respectively. Conclusion: Pembrolizumab may be effective against G-CSF-producing NSCLC with high PD-L1 expression. Corticosteroids seemed to inhibit inflammation induced by the tumor, and exert the efficacy of pembrolizumab.

Small cell lung cancer (SCLC) and large cell neuroendocrine carcinoma (LCNEC) have recently been grouped as lung neuroendocrine carcinomas (NECs). Because these lung NECs are clinically malignant and their treatment strategies differ from those of non-SCLC, the quality of diagnosis has a significant prognostic impact. The diagnosis of LCNEC requires positive immunohistochemical staining with chromogranin A, synaptophysin, and CD56, along with a morphological diagnosis, and insulinoma-associated protein 1 (INSM1) has been proposed as an additional marker but is still not an ideal or better marker. We investigated Musashi-1 as a novel immunohistochemical marker in 42 patients with SCLCs and 44 with LCNECs who underwent lung resection between 1998 and 2020 at our institution. We found Musashi-1 expression in 98% (41/42) SCLC and in 90% (40/44) LCNEC. These findings were similar to CD56 expression and superior to synaptophysin, chromogranin A, and INSM1. Musashi-1 also tended to show more diffuse and intense staining, especially in LCNEC, with more cases staining > 10% than any other existing markers (Musashi-1, 77%; INSM1, 45%; chromogranin A, 34%; synaptophysin, 41%; and CD56, 66%). In conclusion, we identified Musashi-1 as a novel immunohistochemical staining marker to aid in the diagnosis of lung NEC.

Small cell lung cancer (SCLC) and large cell neuroendocrine carcinoma (LCNEC) have recently been grouped as lung neuroendocrine carcinomas (NECs). Because these lung NECs are clinically malignant and their treatment strategies differ from those of non-SCLC, the quality of diagnosis has a significant prognostic impact. The diagnosis of LCNEC requires positive immunohistochemical staining with chromogranin A, synaptophysin, and CD56, along with morphological diagnosis, and insulinoma-associated protein 1 (INSM1) has been proposed as an additional marker but sometimes experience difficulty in making the diagnosis. We investigated Musashi-1 as a novel immunohistochemical marker in 42 patients with SCLCs and 44 with LCNECs who underwent lung resection between 1998 and 2020 at our institution. We found Musashi-1 expression in 41 (98%) of 42 SCLCs and 40 (90%) of 44 LCNECs. These findings were similar to CD56 expression and superior to synaptophysin, chromogranin A, and INSM1. Musashi-1 also tended to show more diffuse and intense staining, especially in LCNEC, with more cases staining >10% than any other existing markers (Musashi-1, 77%; INSM1, 45%; chromogranin A, 34%; synaptophysin, 41%; and CD56, 66%). In conclusion, we identified Musashi-1 as a novel immunohistochemical staining marker to aid in the diagnosis of lung NEC.

Introduction: Malignant mesothelioma is an aggressive cancer associated with asbestos exposure. Currently, the efficacy of therapeutics is limited in malignant mesothelioma, and developing more effective therapies is the need of the hour. Non-coding RNAs (ncRNAs), including microRNAs (miRNAs), have attracted attention as therapeutic targets. To explore potential therapeutic targets, we focused on miR-142-3p expression, which was found to be significantly downregulated in mesothelioma cell lines in our previous study. Methods: Mesothelioma cell lines and tissues were validated for expression of miR-142-3p or integrin subunit alpha-V (ITGAV). We transfected mesothelioma cell lines with miR-142-3p mimic and ITGAV siRNA and analyzed their biological functions. Results: We found that miR-142-3p was significantly downregulated in mesothelioma tissues. Transfection with miR-142-3p mimic significantly suppressed cell proliferation, migration, and invasion. Bioinformatics analysis of potential targets of miR-142-3p identified ITGAV. Membrane ITGAV expression in mesothelioma cell lines was confirmed using immunocytochemistry. ITGAV was significantly upregulated in mesothelioma tissues. Moreover, transfection of miR-142-3p mimics into mesothelioma cell lines significantly suppressed ITGAV expression, indicating that miR-142-3p targets ITGAV. Next, ITGAV siRNA transfection into mesothelioma cell lines inhibited cell proliferation, migration, and invasion. Further investigation of cell adhesion mechanisms showed that the miR-142-3p/ITGAV axis specifically affects mesothelioma cell adhesion via vitronectin in the extracellular matrix. Conclusion: This study proposed that the miR-142-3p/ITGAV axis is involved in tumor progression in malignant mesothelioma.

Although the routine use of immunohistochemistry has improved the accuracy of histopathologic diagnosis in clinical practice, new methods for discovering novel diagnostic markers are still needed. We sought new diagnostic markers for malignant pleural mesothelioma (MPM) using a reverse translational approach with limited archival tissues from a very rare case. Total RNA extracted from formalin-fixed paraffin-embedded (FFPE) tissues of a synchronous collision tumor consisting of MPM and pulmonary adenocarcinoma (PAC) was employed for gene expression profiling (GEP) analysis. Among the 54 genes selected by GEP analysis, we finally identified the following two candidate MPM marker genes: PHGDH and TRIM29. Immunohistochemical analysis of 48 MM and 20 PAC cases showed that both PHGDH and TRIM29 had sensitivity and specificity almost equivalent to those of calretinin (sensitivity 50% and 46% vs. 63%, and specificity 95% and 100% vs. 100%, respectively). Importantly, of the 23 epithelioid MMs, all 3 calretinin-negative cases were positive for TRIM29. These two markers may be diagnostically useful for immunohistochemical distinction between MPMs and PACs. This successful reverse translational approach based on FFPE samples from one very rare case encourages the further use of such samples for the development of novel diagnostic markers.

Sarcomatoid carcinoma (SC) is a rare malignant tumor with properties of both epithelial and mesenchymal carcinomas. SC has been reported in various organs, but the number of reports for each type is small. Small intestinal tumors make up about 3–6% of gastrointestinal malignancies. Discovering them in the early stage is rare and difficult, with anemia and/or abdominal pain as the major symptoms of small intestinal tumors. Primary small intestinal SC (SISC) is rare among small intestinal tumors, and currently very few cases have been reported in the literature. Previous studies have reported that neither chemotherapy nor radiotherapy improves the overall survival rate of patients with SISC, and the prognosis is extremely poor. Currently, surgical resection remains the only optimal therapeutic approach for SISC. Here, we present the case of a 90-year-old woman who had acute peritonitis due to perforation of a small intestinal tumor. She underwent emergency exploratory laparotomy and partial resection of the small intestine, including the tumor. The tumor was pathologically identified as a primary SISC with mesenteric lymph node metastasis. Subsequently, she had recurrence in the intra-abdominal area and lymph node metastasis anterior to the inferior vena cava and died 15 months after surgery without any additional treatment.

Malignant pleural mesothelioma is a notorious human malignancy. Despite combination chemotherapy with cisplatin and pemetrexed, the majority of patients with advanced malignant pleural mesothelioma have a poor prognosis. MicroRNAs (miRNAs/miRs) are short non‑coding RNAs that regulate various biological processes by binding to the 3'‑untranslated region of target gene mRNAs and suppressing their expression. Since abnormal expression patterns of miRNAs are a common feature in human malignancies, a number of them have been researched as potential therapeutic targets. Our previous study demonstrated that microRNA‑18a (miR‑18a) is upregulated in mesothelioma cell lines compared with in non‑neoplastic mesothelial tissues, but its function remains unclear. In the present study, miRNA inhibitor was transfected into mesothelioma cell lines and then analyzed various cellular functions. Mesothelioma cells transfected with the miR‑18a inhibitor exhibited lower proliferation and migration rates compared with cells transfected with a negative control inhibitor in proliferation and wound scratch assays, respectively. Additionally, the present study revealed that downregulation of miR‑18a increased mesothelioma cell apoptosis. In a chemosensitivity assay, transfection of the miR‑18a inhibitor significantly increased the sensitivity of mesothelioma cells to cisplatin but not to pemetrexed. Therefore, miR‑18a may be a potential therapeutic target for mesothelioma resistant to cisplatin.

Aims The process of differential diagnosis between epithelioid mesothelioma and lung adenocarcinoma has been progressing; however, there are no absolute immunohistochemical markers with which to definitively diagnose epithelioid mesothelioma. The aim of this study was to search for a novel negative marker of epithelioid mesothelioma. Methods and results We immunohistochemically studied the applicability of mucin 21 (MUC21), which was identified in our previous study, as a novel, negative diagnostic marker for epithelioid mesothelioma. Seventy epithelioid mesotheliomas and 70 lung adenocarcinomas were investigated for the expression of MUC21, along with other previously reported markers, by the use of immunohistochemistry. MUC21 was expressed in only two of the 70 (3%) epithelioid mesotheliomas, as compared with 67 of the 70 (96%) lung adenocarcinomas. The sensitivity, specificity and accuracy of negative MUC21 expression for differentiating epithelioid mesothelioma from lung adenocarcinoma were 97%, 96%, and 96%, respectively; these are similar to those of carcinoembryonic antigen and claudin‐4, and better than those of thyroid transcription factor‐1, napsin‐A, and mucin 4. Conclusion MUC21 could be used as an additional, novel, negative immunohistochemical marker to differentiate mesothelioma from lung adenocarcinoma.