Successful reconstruction using a buccal fat pad flap in misdiagnosed buccinators intramuscular synovial sarcoma: A case report.

INTRODUCTION: Synovial sarcoma (SS) is a subtype of soft tissue sarcoma that primarily usually occurs in the lower extremities but rarely arises in the head and neck areas, including the oral cavity. Due to its variable presentation and similarity to benign masses in terms of age at onset, growth rate, and favorable outcomes, SS is often misdiagnosed as a benign tumor. However, it is a malignant tumor. PATIENT CONCERNS: We report the case of intramuscular SS in the oral cavity. Initially, the lesion was clinically suspected as a benign mass but was ultimately confirmed as malignant SS. DIAGNOSIS: Although histopathological examination is the first step in diagnosing SS, molecular testing to confirm the presence of SYT-SSX fusion can provide a definitive diagnosis when the histopathology is inconclusive. In this patient as well, the postoperative pathological report confirmed the diagnosis of biphasic SS, and molecular testing revealed positive SYT/SSX fusion. THERAPEUTICS INTERVENTIONS: Following the recommendation of multidisciplinary care system, a wide excision was performed including the buccinators muscle, and reconstruction was performed using a buccal fat pad flap to prevent cheek depression. OUTCOMES: On the final pathologic report, SS was removed margin-free, and there were no metastatic lymph nodes. No evidence of cheek dimpling was observed, and follow-up neck CT showed no significant changes in the lymph nodes. As a result of observation up to several months after surgery, there were no functional and aesthetic complications. CONCLUSIONS: We report a successful case of intramuscular SS resection, initially misdiagnosed as a benign mass, using a buccal fat pad flap. We also highlight the importance of correctly diagnosing SS, especially in the craniofacial region where it can be mistaken for benign masses.

Combined Intramedullary and Intradural Extramedullary Solitary Fibrous Tumor in Cervical Spine

We present a rare case of solitary fibrous tumor (SFT) located in the intramedullary (IM) and intradural extramedullary sites of cervical spine, mimicking thrombosed aneurysm and meningioma. Herein, we present a case of spinal intradural SFT in a 59-year-old woman. She presented to the outpatient clinic with a right-sided motor weakness for over a year. The case was initially misinterpreted as a thrombosed aneurysm of the posterior spinal artery. Cervical spine magnetic resonance imaging revealed a well-circumscribed intradural mass with isosignal intensity on T1 and T2-weighted images with markedly T2 dark signal focus and homogenous intense enhancement at the level of C6. Computed tomography showed a slightly high-density mass without evidence of calcification or cystic component. Surgical removal was performed. However, due to combined IM component with adhesion, incomplete tumor resection was done. Pathologic analysis revealed hypocellular spindle cells with a thick collagenous stroma and immunohistochemical staining confirmed SFT. Spinal intradural SFT is a rare spindle cell tumor. Radiologists should consider SFT as a differential diagnosis if T2-weighted imaging shows an intradural located mass with markedly dark signal intensity focus.

A Rare Variant of Mazabraud’s Syndrome Overlapping with McCune-Albright Syndrome with a Clinical Review: A Case Report

Mazabraud syndrome (MS) is a rare and sporadic disorder. It is mainly characterized by fibrous dysplasia (FD) of single or multiple bones and intramuscular myxomas (IM). Data on the prevalence since it was first reported, clinical features, and prognosis are extremely scarce. We report a case of a 59-year-old woman with IM and polyostotic FD. She also had multiple cafe’-au-lait spots suggestive of McCune-Albright syndrome (MAS). On magnetic resonance imaging, there are masses with well-defined heterogeneous enhancement, accompanied by an inner cyst in the vastus lateralis muscle and femur. These radiological results are identical to those of FD. After surgical intervention with excision of intramuscular soft-tissue mass, a diagnosis of IM of MS was confirmed. Given that cafe’-au-lait spots also appeared, the patient was diagnosed with a variant of MS with some of the clinical characteristics of MAS.

Severity of foot process effacement is associated with proteinuria in patients with IgA nephropathy

Background@#Proteinuria is a significant risk factor for progression of IgA nephropathy (IgAN) and has a positive correlation with severity of foot process effacement (FPE). We evaluated the relationship of FPE with proteinuria and histologic characteristics, including the Oxford classification. @*Methods@#Patients who underwent renal biopsy and were diagnosed with IgAN at a single center were retrospectively reviewed. Patients aged less than 18 years and those with the possibility of secondary causes were excluded from the study. Subsequently, we evaluated the association between degree of proteinuria, severity of FPE, and histologic characteristics, including the Oxford classification and other immunofluorescence stains. @*Results@#A total of 805 cases of renal biopsy was performed at our institution, and 327 patients were diagnosed with IgAN. Among them, 82 patients were excluded. Severity of FPE had an impact on the degree of proteinuria. Notably, the group with diffuse FPE had more than about 1.3 g/day of urine protein compared to those with rare FPE. Among the histologic characteristics, M1 score and immune deposition of IgG affected severity of FPE (hazard ratios [95% confidence interval], 1.90 [1.10 to 3.26], and 3.77 [1.66 to 8.54], respectively). @*Conclusion@#Severity of FPE had an impact on the degree of proteinuria and may be associated with the pathogenesis of IgAN.

Clinicopathological Significance of Large Tumor Suppressor (LATS) Expression in Gastric Cancer

PURPOSE: The aims of this study were to evaluate the expression of the large tumor suppressor (LATS) genes LATS1 and LATS2 by immunohistochemical staining of gastric cancer, and to evaluate the clinicopathological significance of LATS expression and its correlation with overall survival (OS). MATERIALS AND METHODS: LATS1 and LATS2 expression in a tissue microarray was detected by immunohistochemistry, using 264 gastric cancer specimens surgically resected between July 2006 and December 2009. RESULTS: Low expression of LATS1 was significantly associated with more advanced American Joint Committee on Cancer (AJCC) stage (P=0.001) and T stage (P=0.032), lymph node (LN) metastasis (P=0.040), perineural invasion (P=0.042), poor histologic grade (P=0.007), and diffuse-type histology by the Lauren classification (P=0.033). Low expression of LATS2 was significantly correlated with older age (≥65, P=0.027), more advanced AJCC stage (P=0.001) and T stage (P=0.001), LN metastasis (P=0.004), perineural invasion (P=0.004), poor histologic grade (P<0.001), and diffuse-type histology by the Lauren classification (P<0.001). Kaplan-Meier survival analysis revealed significantly poor OS rates in the groups with low LATS1 (P=0.037) and LATS2 (P=0.037) expression. CONCLUSIONS: Expression of LATS1 or LATS2 is a significant marker for a good prognosis in patients with gastric cancer.

Clinicopathologic and Prognostic Significance of Transducin-Like Enhancer of Split 1 Protein Expression in Invasive Breast Cancer / 한국유방암학회지

PURPOSE: Transducin-like enhancer of split 1 (TLE1) is a member of the TLE family of transcriptional co-repressors that control the transcription of a wide range of genes. We investigated the prognostic significance of TLE1 protein expression in breast cancers by using immunohistochemistry and explored the relationship of TLE1 with clinicopathological parameters. METHODS: Immunohistochemistry was performed on 456 cases of breast cancer tiled on tissue microarrays. The relationship between TLE1 expression in normal breast specimens and ductal carcinoma in situ (DCIS) was also analyzed. RESULTS: TLE1 was highly expressed in 57 of 456 (12.5%) carcinoma samples. TLE1 was more frequently expressed in DCIS and invasive breast cancers than in normal breast tissue (p=0.002). High expression of TLE1 significantly correlated with negative lymph node (LN) metastasis (p=0.007), high histologic grade (p<0.001), estrogen receptor negativity (p<0.001), progesterone receptor negativity (p<0.001), human epidermal growth factor receptor 2 (HER2) positivity (p<0.001), and high Ki-67 proliferation index (p<0.001). Based on intrinsic subtypes, high TLE1 expression was strongly associated with HER2+ and triple-negative breast cancers (TNBC) (p<0.001). Survival analysis demonstrated no significant association between TLE1 expression and disease-free survival (DFS) (p=0.167) or overall survival (OS) (p=0.286). In subgroup analyses, no correlation was found between TLE1 expression and DFS or OS according to LN status or intrinsic subtype. CONCLUSION: High TLE1 expression is significantly associated with the HER2+ and TNBC subtypes. This is the first study documenting immunohistochemical expression of TLE1 in invasive breast cancer and its association with clinicopathological parameters, prognosis, and intrinsic subtype.

High EZH2 Protein Expression Is Associated with Poor Overall Survival in Patients with Luminal A Breast Cancer / 한국유방암학회지

PURPOSE: The enhancer of zeste homologue 2 (EZH2) is a catalytic subunit of the polycomb repressive complex 2, a highly conserved histone methyltransferase. EZH2 overexpression has been implicated in various malignancies, including breast cancer, where is associated with poor outcomes. This study aims to clarify nuclear EZH2 expression levels in breast cancers using immunohistochemistry (IHC) and correlate these findings with clinicopathologic variables, including prognostic significance. METHODS: IHC was performed on tissue microarrays of 432 invasive ductal carcinoma (IDC) tumors. Associations between EZH2 expression, clinicopathologic characteristics, and molecular subtype were retrospectively analyzed. The relationship between EZH2 protein expression in normal breast tissue and ductal carcinoma in situ (DCIS) was also assessed. RESULTS: High EZH2 expression was demonstrated in 215 of 432 tumors (49.8%). EZH2 was more frequently expressed in DCIS and IDC than in normal breast tissue (p=0.001). High EZH2 expression significantly correlated with high histologic grade (p<0.001), large tumor size (p=0.014), advanced pathologic stage (p=0.006), negative estrogen receptor status (p<0.001), positive human epidermal growth factor receptor 2 (HER2) status (p<0.001), high Ki-67 staining index (p<0.001), positive cytokeratin 5/6 status (p=0.003), positive epidermal growth factor receptor status (p<0.001), and positive p53 status (p<0.001). Based on molecular subtypes, high EZH2 expression was significantly associated with HER2-negative luminal B, HER2-positive luminal B, and HER2 type and triple-negative basal cancers (p<0.001). In patients with luminal A, there was a significant trend toward shorter overall survival for those with tumors having high EZH2 expression compared to those with tumors having low EZH2 expression (p=0.045). CONCLUSION: EZH2 is frequently upregulated in breast malignancies, and it may play an important role in cancer development and progression. Furthermore, EZH2 may be a prognostic marker, especially in patients with luminal A cancer.

Clinicopathological Significance of Elevated PIK3CA Expression in Gastric Cancer

PURPOSE: PIK3CA is often mutated in a variety of malignancies, including colon, gastric, ovary, breast, and brain tumors. We investigated PIK3CA expression in gastric cancer and explored the relationships between the PIK3CA expression level and clinicopathological features as well as survival of the patients. MATERIALS AND METHODS: We examined PIK3CA expression in a tissue microarray of 178 gastric adenocarcinomas by immunohisto-chemistry and reviewed patients' medical records. RESULTS: In our study, 112 of the 178 gastric cancer patients displayed positive PIK3CA expression. Overexpression of PIK3CA was correlated with low grade differentiation (P=0.001), frequent lymphatic invasion (P=0.032), and high T stage (P=0.040). Patients with positive PIK3CA staining were more likely to display worse overall survival rate than those with negative PIK3CA staining, as determined by Kaplan-Meier survival analysis with log-rank test (P=0.047) and a univariate analysis using the Cox proportional hazard model (hazard ratio=1.832, P=0.051). CONCLUSIONS: Elevated PIK3CA expression was significantly correlated with tumor invasiveness, tumor phenotypes, and poor patient survival.

A Rare Radiological Presentation of Pulmonary Mucosa-Associated Lymphoid Tissue Lymphoma as Bronchovascular Thickening and Ground Glass Opacities with Concurrent Pancreas Involvement

Pulmonary mucosa-associated lymphoid tissue (MALT) lymphoma is a rare disease and usually presents as pulmonary masses, mass-like consolidation, or pulmonary nodules on chest images. We report a case of a 43-year-old man with symptoms of chronic cough for 1 year, showing bilateral diffuse bronchovascular bundle thickening and focal ground glass opacities on a chest computed tomography scan. Video-assisted thoracoscopic surgery was performed and the final pathologic diagnosis was pulmonary MALT lymphoma. Concurrent involvement of the pancreas was discovered during staging workup. After diagnosis, he was treated with cytotoxic chemotherapy and rituximab and showed improvements in his lung lesion and pancreas.

A Case of Persistent Gestational Trophoblastic Disease after Complete Hydatidiform Mole

Gestational trophoblastic disease is an abnormal proliferations of trophoblastic tissue during pregnancy. Persistent gestational trophoblastic tumor develops in about 20% after evacuation of complete mole. Following evacuation of hydatidiform mole, the interpretation of serial serum human chorionic gonadotropin (hCG) regression patterns is important in monitoring the course of the disease. Because it is the most reliable and sensitive method for the early detection of gestational trophoblastic disease. We describe an uncommon case of complete hydatidiform mole in a 48-year-old woman, who has presented to us with complaints of bleeding. She experienced after the evacuation of a complete mole and no decreased in hCG levels over four consecutive serum hCG measurements. The patient underwent hysterectomy due to leiomyoma. Finally, pathologic diagnosis was confirmed persistent gestational trophoblastic disease.

Expression of Programmed Death Receptor Ligand 1 with High Tumor-Infiltrating Lymphocytes Is Associated with Better Prognosis in Breast Cancer / 한국유방암학회지

PURPOSE: The interaction of programmed death receptor 1 (PD-1) and its ligand, programmed death receptor ligand 1 (PD-L1), negatively regulates immune responses. This study aimed to clarify PD-L1 expression levels in breast cancer through immunohistochemistry (IHC) and to evaluate associations between these findings and clinicopathologic variables, including prognosis. METHODS: PD-L1 expression was analyzed using IHC on tissue microarrays of 465 invasive breast carcinomas. RESULTS: High PD-L1 expression was demonstrated in 63 of 465 tumors (13.5%). High PD-L1 expression was significantly associated with high histologic grade (p<0.001), negative lymph nodes (p=0.011), early pathologic stage (p=0.025), high tumor-infiltrating lymphocyte (TIL) (p<0.001) counts, negative estrogen receptor (p<0.001) and progesterone receptor (p=0.002) expression, positive human epidermal growth factor receptor 2 (HER2) (p=0.003), cytokeratin 5/6 (p=0.011), epidermal growth factor receptor (p<0.001), and p53 (p<0.001) expression, and high Ki-67 proliferating index (p<0.001). Based on intrinsic subtypes, high PD-L1 expression and high TIL counts were significantly associated with the HER2 and triple-negative basal type (p<0.001). PD-L1 expression was significantly associated with better disease-free survival (DFS) (p=0.041) and overall survival (OS) (p=0.026) in the univariate analysis, but not in the multivariate analysis. Higher TIL levels was an independent prognostic factor for decreased disease progression (hazard ratio [HR], 2.389; 95% confidence interval [CI], 1.284–4.445; p=0.006) and overall death (HR, 3.666; 95% CI, 1.561–8.607; p=0.003). CONCLUSION: PD-L1 protein expression in breast cancer is associated with better DFS and OS, but is not an independent prognostic factor. High PD-L1 expression was significantly associated with high TIL levels. This finding has important implications for antibody therapies targeting the PD-1/PD-L1 signaling mechanism in breast cancer.

Prognostic and Clinicopathological Significance of Transducer-Like Enhancer of Split 1 Expression in Gastric Cancer

PURPOSE: Transducer-like enhancer of split 1 (TLE1) is a member of the Groucho/TLE family of transcriptional co-repressors that regulate the transcriptional activity of numerous genes. TLE1 is involved in the tumorigenesis of various tumors. We investigated the prognostic significance of TLE1 expression and its association with clinicopathological parameters in gastric cancer (GC) patients. MATERIALS AND METHODS: Immunohistochemical analysis of six tissue microarrays was performed to examine TLE1 expression using 291 surgically resected GC specimens from the Soonchunhyang University Cheonan Hospital between July 2006 and December 2009. RESULTS: In the non-neoplastic gastric mucosa, TLE1 expression was negative. In GC, 121 patients (41.6%) were positive for TLE1. The expression of TLE1 was significantly associated with male gender (P=0.021), less frequent lymphatic (P=0.017) or perineural invasion (P=0.029), intestinal type according to the Lauren classification (P=0.024), good histologic grade (P<0.001), early pathologic T-stage (P=0.012), and early American Joint Committee on Cancer stage (P=0.022). In the Kaplan-Meier analysis, the TLE1 expression was significantly associated with longer disease-free (P=0.022) and overall (P=0.001) survival rates. CONCLUSIONS: We suggested that TLE1 expression is a good prognostic indicator in GCs.

Loss of FAT Atypical Cadherin 4 Expression Is Associated with High Pathologic T Stage in Radically Resected Gastric Cancer

PURPOSE: Recent studies have revealed recurrent alterations in the cell adhesion gene FAT4, a candidate tumor suppressor gene, in cancer. FAT atypical cadherin 4 (FAT4) is a transmembrane receptor involved in the Hippo signaling pathway, which is involved in the control of organ size. Here, we investigated the loss of FAT4 expression and its association with clinicopathological risk factors in gastric cancer. MATERIALS AND METHODS: We assessed the expression of FAT4 by using immunohistochemistry on three tissue microarrays containing samples from 136 gastric cancer cases, radically resected in the Soonchunhyang University Cheonan Hospital between July 2006 and June 2008. Cytoplasmic immunoexpression of FAT4 was semi-quantitatively scored using the H-score system. An H-score of > or =10 was considered positive for FAT4 expression. RESULTS: Variable cytoplasmic expressions of FAT4 were observed in gastric cancers, with 33 cases (24.3%) showing loss of expression (H-score or =10, 36.4% vs. 16.5%, P=0.015), high pathologic T stage (P=0.015), high tumor-node-metastasis stage (P=0.017), and reduced disease-free survival time (H-score or =10, mean survival 62.7+/-7.3 months vs. 79.1+/-3.1 months, P=0.025). However, no association was found between the loss of FAT4 expression and tumor size, gross type, histologic subtype, Lauren classification, lymphovascular invasion, or overall survival. CONCLUSIONS: Loss of FAT4 expression appears to be associated with invasiveness in gastric cancer.

Loss of Tumor Suppressor ARID1A Protein Expression Correlates with Poor Prognosis in Patients with Primary Breast Cancer / 한국유방암학회지

PURPOSE: Somatic mutations of the chromatin remodeling AT-rich interactive domain 1A (SWI-like) gene (ARID1A) have been identified in many human cancers, including breast cancer. The purpose of this study was to evaluate the nuclear expression of ARID1A in breast cancers by immunohistochemistry (IHC) and to correlate the findings to clinicopathologic variables including prognostic significance. METHODS: IHC was performed on tissue microarrays of 476 cases of breast cancer. Associations between ARID1A expression and clinicopathologic characteristics and molecular subtype were retrospectively analyzed. RESULTS: Low expression of ARID1A was found in 339 of 476 (71.2%) cases. Low expression of ARID1A significantly correlated with positive lymph node metastasis (p=0.027), advanced pathologic stage (p=0.001), low Ki-67 labeling index (p=0.003), and negative p53 expression (p=0.017). The ARID1A low expression group had significantly shorter disease-free and overall survival than the ARID1A high expression group (p<0.001 and p<0.001, respectively). Multivariate analysis demonstrated that low expression of ARID1A was a significant independent predictive factor for poor disease-free and overall survival in patients with breast cancer (disease-free survival: hazard ratio, 0.38, 95% confidence interval [CI], 0.20-0.73, p=0.004; overall survival: hazard ratio, 0.11, 95% CI, 0.03-0.46, p=0.003). In patients with luminal A type disease, patients with low ARID1A expression had significantly shorter disease-free and overall survival rates than patients with high ARID1A expression (p=0.022 and p=0.018, respectively). CONCLUSION: Low expression of ARID1A is an independent prognostic factor for disease-free and overall survival in breast cancer patients and may be associated with luminal A type disease. Although the biologic function of ARID1A in breast cancer remains unknown, low expression of ARID1A can provide valuable prognostic information.

Loss of ARID1A Expression in Gastric Cancer: Correlation with Mismatch Repair Deficiency and Clinicopathologic Features

PURPOSE: The AT-rich interactive domain 1A (ARID1A) gene encodes BRG1-associated factor 250a, a component of the SWItch/Sucrose NonFermentable chromatin remodeling complex, which is considered a tumor suppressor in many tumors. We aimed to investigate the prognostic significance of ARID1A expression in gastric cancers and explore its relationship with clinicopathologic parameters such as mismatch repair protein expression. MATERIALS AND METHODS: Four tissue microarrays were constructed from 191 resected specimens obtained at Soonchunhyang University Cheonan Hospital from 2006 to 2008. Nuclear expression of ARID1A was semiquantitatively assessed and binarized into retained and lost expression. RESULTS: Loss of ARID1A expression was observed in 62 cases (32.5%). This was associated with more frequent vascular invasion (P=0.019) and location in the upper third of the stomach (P=0.001), and trended toward more poorly differentiated subtypes (P=0.054). ARID1A loss was significantly associated with the mismatch repair-deficient phenotype (P=0.003). ARID1A loss showed a statistically significant correlation with loss of MLH1 (P=0.001) but not MSH2 expression (P=1.000). Kaplan-Meier survival analysis showed no statistically significant difference in overall survival; however, patients with retained ARID1A expression tended to have better overall survival than those with loss of ARID1A expression (P=0.053). In both mismatch repair-deficient and mismatch repair-proficient groups, survival analysis showed no differences related to ARID1A expression status. CONCLUSIONS: Our results demonstrated that loss of ARID1A expression is closely associated with the mismatch repair-deficient phenotype, especially in sporadic microsatellite instability-high gastric cancers.

A Rare Case of Primary Tubular Adenocarcinoma of the Thymus, Enteric Immunophenotype: A Case Study and Review of the Literature

Thymic carcinomas are uncommon malignant tumors, and thymic adenocarcinomas are extremely rare. Here, we describe a case of primary thymic adenocarcinoma in a 59-year-old woman. Histological examination of the tumor revealed tubular morphology with expression of cytokeratin 20 and caudal-type homeobox 2 according to immunohistochemistry, suggesting enteric features. Extensive clinical and radiological studies excluded the possibility of an extrathymic primary tumor. A review of the literature revealed only two global cases of primary tubular adenocarcinomas of the thymus with enteric immunophenotype.

Mediastinal Glomus Tumor: A Case Report and Literature Review

A glomus tumor in the mediastinum is very uncommon, and only five cases have been reported in the English literature. We recently encountered a 21-year-old woman with an asymptomatic mediastinal mass that measured 5.3 x 4.0 cm. Surgical excision was performed, and the tumor was finally diagnosed as mediastinal glomus tumor with an uncertain malignant potential. After reviewing this case and previous reports, we analyzed the clinicopathologic features associated with progression of such a tumor.

Diagnostic and Therapeutic Approach for Acute Paraquat Intoxication

Paraquat (PQ) has known negative human health effects, but continues to be commonly used worldwide as a herbicide. Our clinical data shows that the main prognostic factor is the time required to achieve a negative urine dithionite test. Patient survival is a 100% when the area affected by ground glass opacity is <20% of the total lung volume on high-resolution computed tomography imaging 7 days post-PQ ingestion. The incidence of acute kidney injury is approximately 50%. The average serum creatinine level reaches its peak around 5 days post-ingestion, and usually normalizes within 3 weeks. We obtain two connecting lines from the highest PQ level for the survivors and the lowest PQ level among the non-survivors at a given time. Patients with a PQ level between these two lines are considered treatable. The following treatment modalities are recommended to preserve kidney function: 1) extracorporeal elimination, 2) intravenous antioxidant administration, 3) diuresis with a fluid, and 4) cytotoxic drugs. In conclusion, this review provides a general overview on the diagnostic procedure and treatment modality of acute PQ intoxication, while focusing on our clinical experience.

Struma Ovarii: A Case of Struma Ovarii and Literature Review

Struma ovarii is a rare, monodermal and highly specialized teratoma, composed entirely or predominantly (>50%) of thyroid tissue. Presenting symptoms are not specific. Despite containing thyroid tissue, only 5% of struma ovarii have features of hyperthyroidism. Therefore, preoperative diagnosis of struma ovarii is difficult. Recently, the authors experienced a case of struma ovarii found in a young woman who presented with known pelvic mass and dysmenorrhea. A transabdominal ultrasonography and computed tomography detected a 16-cm sized multiloculated mass in pelvic cavity. She underwent laparoscopic unilateral ovarian wedge resection. The final histopathologic diagnosis was struma ovarii of the mature cystic teratoma. Therefore, we report this rare case with a brief review of the literature.

A Case Report of IgG4-Related Disease Clinically Mimicking Pleural Mesothelioma / 결핵및호흡기질환

An immunoglobulin G4 (IgG4)-related disease is a recently emerging entity, and a few cases of IgG4-related disease in lung and pleura have been reported. Herein, we report the case of a 74-year-old man with IgG4-related disease of lung and pleura, clinically suspicious of malignant mesothelioma. Chest computed tomography showed diffuse nodular pleural thickening, and microscopic finding disclosed diffuse thickening of visceral pleura with infiltrations of many lymphoplasma cells with increased number of IgG4-positive plasma cells and a few multinucleated giant cells. It is important for pathologists and clinicians to recognize this rare entity and its histologic finding, because it can be confused with malignant tumors on the radiologic examination although it can be treated with steroid therapy.