Keiko Mitani

Lymphangiogenesis-mediated shedding of LAM cell clusters as a mechanism for dissemination in lymphangioleiomyomatosis.

Lymphangioleiomyomatosis (LAM) affects exclusively women of reproductive age, involves the lungs and axial lymphatic system, and is frequently complicated with renal angiomyolipomas. LAM lesions are generated by the proliferation of LAM cells with mutations of one of the tuberous sclerosis complex (TSC) genes. Recent studies indicate that LAM cells can migrate or metastasize to form new lesions in multiple organs, although they show a morphologically benign appearance. In the previous study, we reported LAM-associated lymphangiogenesis and implicated its role in the progression of LAM. In this study, we further focused on the lymphatic abnormalities in LAM: LAM-associated chylous fluid (5 pleural effusion and 2 ascites), surgically resected diaphragm (1 patient), and axial lymphatic system including the thoracic duct, lymph nodes at various regions, and diaphragmatic lymphatic system (5 autopsy cases). We demonstrated that LAM cell clusters enveloped by lymphatic endothelial cells (LCC) in all chylous fluid examined. We identified LAM lesion in the diaphragm (2 of 5 autopy cases and one surgical specimen), thoracic duct (5 of 5), and lymph nodes (retroperitoneal (5 of 5), mediastinal (4 of 5), left venous angle (5 of 5) with total positive rate of 68% to 88% at each region of the lymph node, but less frequent or none at remote lymph nodes located away from the axial lymph trunk (cervical [1 of 5] and axillary [0 of 5]). LCCs were identified in intra-LAM lesional lymphatic channels where LAM cells proliferate along lymphatic system. In in vitro culture system, LCC can fragment into each proliferating LAM cell. These findings suggest that LAM-associated lymphangiogenesis demarcates LAM lesion into bundle- or fascicle-like structure and eventually shed LCC into the lymphatic circulation and that LCCs play a central role in the dissemination of LAM lesion.

Lymphangiogenesis in Lymphangioleiomyomatosis Its Implication in the Progression of Lymphangioleiomyomatosis

Lymphangioleiomyomatosis (LAM) is characterized by the proliferation of abnormal smooth muscle cells (LAM cells) in the lungs, lymph nodes, and/or other organs. We examined lymphangiogenesis using immunohistochemistry for Flt-4 (VEGFR-3), a new specific marker for lymphatic endothelial cells, as well as the expression of vascular endothelial growth factor (VEGF)-C in LAM. Specimens were obtained from 6 autopsy cases, a single lung transplant case, and 8 surgical cases for analyses. We demonstrated that lymphatics were extremely abundant in both pulmonary and extrapulmonary LAM and that lymphatic endothelial cells not only proliferated encompassing LAM foci but also infiltrated the intra-LAM foci, and that in advanced LAM, lymphangiogenesis involved vascular walls and interstitium surrounding the area where LAM cells proliferate. In contrast, angiogenesis, confirmed with CD31 immunostaining, was observed less in the LAM foci. LAM cells demonstrated positive reactivity against anti-VEGF-C antibody at varying intensities. Significant correlation (P < 0.001) was noted between the degree of lymphangiogenesis in LAM or VEGF-C expression on LAM cells and lymphagioleiomyomatosis histologic score (LHS), which represents the histologic severity of pulmonary LAM and has been reported to have prognostic significance. Our study is likely to provide a novel point of view on the pathophysiologic significance of lymphangiogenesis in LAM.

Prevalence of Uterine and Adnexal Involvement in Pulmonary Lymphangioleiomyomatosis: A Clinicopathologic Study of 10 Patients

Lymphangioleiomyomatosis (LAM), a systemic disorder affecting almost exclusively young women, is characterized by the abnormal proliferation of smooth muscle-like cells (LAM cells). LAM can occur either in association with the tuberous sclerosis complex (TSC) (TSC-LAM) or without TSC (sporadic LAM). Recent studies have demonstrated that LAM is a neoplasm arising from constitutive activation of the mammalian target of rapamycin signaling pathway dysregulated by a functional loss of TSC genes, but the primary organ of origin remains unclear. Therefore, we performed histologic and immunohistologic analyses of gynecologic organs in 20 patients, half with and the other half without pulmonary LAM, to determine how often LAM involves the uterus. The results showed that 9 of 10 (90%) patients with pulmonary LAM had uterine LAM lesions. In contrast, no patients without pulmonary LAM had so. All uterine LAM lesions were accompanied by LAM lesions in retroperitoneal or pelvic lymph nodes and LAM cell clusters, each enveloped by a monolayer of vascular endothelial growth factor receptor-3–positive lymphatic endothelial cells. Furthermore, when we compared uterine lesions of TSC-LAM with those of sporadic LAM, proliferation of HMB45-positive epithelioid-shaped LAM cells and infiltrates with a tongue-like growth pattern was more prominent in the former, whereas the extent of lymphangiogenesis within the myometrium was greater in the latter. These results indicate that uterine involvement is a common manifestation of LAM, and, possibly, that the uterus or an adjacent locale in the retroperitoneum or pelvic cavity is the primary site of origin of LAM.

Lymphangioleiomyomatosis: a disease involving the lymphatic system.

BACKGROUND Lymphangioleiomyomatosis (LAM) is a rare neoplastic disease in which abnormal smooth muscle-like cells (LAM cells) proliferate in the lungs and along the axial lymphatic systems, including the lymph nodes and thoracic ducts. LAM cells are transformed due to loss-of-function type mutations of either the TSC1 or TSC2 tumor suppressor genes. The pathological features include the proliferation of benign-looking LAM cells and the existence of abundant lymphatic vessels that are associated with clinical conditions such as chyle leakage. LAM cells produce potent lymphangiogenic growth factors (VEGF-C and VEGF-D) and the lymphatic vessel density within LAM lesions correlates with the histologic severity of LAM. The serum VEGF-D level increases in LAM, especially in patients with lymphatic involvement. LAM cell clusters (LCCs), which are postulated pathologically to be generated by lymphangiogenesis-mediated fragmentation and subsequent shedding into the lymphatic circulation, are observed in both chylous effusion and LAM-associated lymphatics within LAM tissue specimens. The identification of LCCs in chylous effusion together with the characteristic clinical manifestations can therefore be an alternative for a lung biopsy if LAM patients are complicated with chylous effusion. CONCLUSION LAM appears to be a disease involving a dysfunction of the lymphatic system and a fascinating model of tumor dissemination that is exclusively lymphangitic. LAM-associated lymphangiogenesis that mediates the shedding of LCCs seems to play a central role in the dissemination of LAM cells and progression in LAM and it may also be a potential therapeutic target as well as the dysregulated mTOR signaling pathway.

Distinct clinicopathological features of NAB2-STAT6 fusion gene variants in solitary fibrous tumor with emphasis on the acquisition of highly malignant potential

The impact of NGFI-A binding protein 2 (NAB2)-signal transducer and activator of transcription 6 (STAT6) fusion on the biological behavior and the mechanism of acquisition of malignant phenotype in solitary fibrous tumor (SFT) is not well understood. We examined variations of the NAB2-STAT6 fusion gene in 40 cases of SFT using formalin-fixed, paraffin-embedded tissues and secondary genetic alterations of tumor protein p53 (TP53),, platelet-derived growth factor receptor, β polypeptide (PDGFRB), and telomerase reverse transcriptase (TERT) promoters. These gene variations were compared with the clinicopathological features. The 2-year and 5-year disease-free survival rates (DFSRs) were 91% and 83%, respectively. All 40 samples demonstrated nuclear staining for STAT6, including CD34-negative cases. Moreover, p53-positive staining was associated with a lower DFSR and was significantly associated with higher Ki-67 label index, higher mitotic rate (mitosis, >4/high-power field), and the presence of nuclear atypia/pleomorphism. NAB2-STAT6 fusions were detected in all of the cases; the NAB2 exon 4-STAT6 exon 2, the most common genotype, appeared in 18 cases, which was associated with thoracic tumor location and the less aggressive phenotype. In contrast, tumors with NAB2 exon 6-STAT6 exon 16/18 demonstrated an aggressive phenotype. Mutations in TP53 and PDGFRB were detected in 2 and 3 cases respectively, and these occurred in a mutually exclusive fashion. TERT promoter hot spot mutations were observed in 5 cases, which were associated with shorter DFSR. Two dedifferentiated SFT cases harbored both TP53 and TERT promoter mutations. TP53 mutations, which result in its overexpression, in combination with TERT promoter mutations seem to play an important role in the dedifferentiation process.

Detection of Epstein–Barr virus-encoded small RNA-expressed myofibroblasts and IgG4-producing plasma cells in sclerosing angiomatoid nodular transformation of the spleen

Sclerosing angiomatoid nodular transformation (SANT) of the spleen is a rare inflammatory tumor-like lesion composed of vascular nodules and non-neoplastic stroma including spindle cells and inflammatory cells. The focus of our study was on the stromal proliferating process in SANT. Nine cases of SANT were examined. All cases showed α-smooth muscle actin (α-SMA) and vimentin on the spindle cells but not CD21, CD31, CD34, CD68, desmin, S100, human herpes virus-8, or anaplastic lymphoma kinase-1. In one case, 20–30% of the myofibroblasts in Epstein–Barr-virus (EBV)-positive spindle cells were detected using double-labeling immunohistochemistry for α-SMA and EBV-encoded small RNA in situ hybridization. A quantitative analysis of IgG and IgG4-positive plasma cells (pPCs) in SANT was performed. The median densities of IgG-pPCs and IgG4-pPCs in SANT were approximately four-fold and 13-fold higher than those in the normal spleens, respectively. In addition, there was a statistically significant increase of IgG4/IgG-pPCs ratio in SANT in comparison to the control specimens. In conclusion, the fibrogenesis in a subset of SANT may be associated with EBV-infected myofibroblasts in an overlapping immune reaction indicated by the presence of infiltrating IgG4-pPCs. Further investigation is needed to elucidate the association between SANT and IgG4-related sclerosing disease.

Different patterns of p16INK4A and p53 protein expressions in intraductal papillary-mucinous neoplasms and pancreatic intraepithelial neoplasia.

Objectives: To examine aberrations and differences of cell cycle regulatory proteins between intraductal papillary-mucinous neoplasms (IPMNs) and pancreatic intraepithelial neoplasias (PanINs). Methods: In total, 47 IPMN lesions and 42 PanIN lesions were obtained from 26 patients with IPMN and 16 patients who underwent pancreatic surgery for invasive pancreatic ductal cancer or other diseases. They were subjected to conventional hematoxylin-eosin staining and immunostaining for p16INK4A and p53. The percentages of immunohistochemical positivity or negativity were compared between IPMN and PanIN, in accordance with the same histological grade of atypia. The Ki-67 labeling index was also counted in each lesion. Results: Either the loss of p16INK4A expression or the overexpression of p53 was much more frequently observed among PanIN-3 than among carcinoma in situ in IPMN (P = 0.046 and 0.008, respectively). The Ki-67 labeling index was correlated with the histological grades of both PanINs and IPMNs (P = 0.0001 and P = 0.0001, respectively). Conclusions: There are different immunohistochemical expression patterns of p16INK4A and p53 between IPMNs and PanINs. These may substantiate their different genetic progressions to invasive carcinoma.Abbreviations: IPMN - intraductal papillary-mucinous neoplasia, PanIN - pancreatic intraepithelial neoplasia

Characterization of pulmonary cysts in Birt–Hogg–Dubé syndrome: histopathological and morphometric analysis of 229 pulmonary cysts from 50 unrelated patients

To characterize the pathological features of pulmonary cysts, and to elucidate the possible mechanism of cyst formation in the lungs of patients with Birt–Hogg–Dubé syndrome (BHDS), a tumour suppressor gene syndrome, using histological and morphometric analyses.

Loss of heterozygosity on tuberous sclerosis complex genes in multifocal micronodular pneumocyte hyperplasia

Multifocal micronodular pneumocyte hyperplasia is a rare pulmonary manifestation of tuberous sclerosis complex (TSC) that is a tumor suppressor gene disorder characterized by many hamartomas. A purported mechanism of hamartomatous proliferation in TSC is constitutive activation of the mammalian target of rapamycin (mTOR) signaling pathway dysregulated by a functional loss of TSC genes. Although multifocal micronodular pneumocyte hyperplasia develops locally as self-limited, benign lesions, it is morphologically similar to the preinvasive lesion of pneumocytes that characterize atypical adenomatous hyperplasia or bronchioloalveolar carcinoma. Frequently both conditions include a loss of heterozygosity on TSC. The goal of this study was to determine whether multifocal micronodular pneumocyte hyperplasia is neoplastic. Loss of heterozygosity on TSC genes and immunohistochemistry for mTOR-related proteins (phospho-mTOR, phospho-p70S6K, phospho-S6, and phospho-Akt) were analyzed in 42 lesions: 16 multifocal micronodular pneumocyte hyperplasia (7 patients with TSC, 1 TSC not confirmed), 14 atypical adenomatous hyperplasia, and 12 bronchioloalveolar carcinoma (9 and 12 patients, respectively). The results showed that at least one of two multifocal micronodular pneumocyte hyperplasia lesions from each patient had loss of heterozygosity on TSC1 or TSC2 (15 or 50%) and were frequently immunopositive for phospho-mTOR (88%), phospho-p70S6K (100%), and phospho-S6 (100%) but not phospho-Akt (14%), an upstream regulatory protein of mTOR. Loss of heterozygosity of TSC was found in the preinvasive lesions of pneumocytes, equal to or less than multifocal micronodular pneumocyte hyperplasia. In contrast, phospho-Akt was expressed in the preinvasive lesions of pneumocytes more frequently than multifocal micronodular pneumocyte hyperplasia, but the other mTOR-related proteins were less frequently expressed in the former than in the latter. These outcomes suggest that functional loss of TSCs and consequent hyperphosphorylation of mTOR-related proteins in multifocal micronodular pneumocyte hyperplasia may cause its benign neoplastic proliferation of pneumocytes.

Expression of Transforming Growth Factor β1, β2, and β3 in Chronic, Cancer-Associated, Obstructive Pancreatitis

Abstract Context.—Myofibroblasts are considered to play central roles in pancreatic fibrosis. The potent fibrogenic capacities of transforming growth factor βs (TGF-βs) have been emphasized in vitro and in animal studies. However, the roles of TGF-βs in human chronic pancreatitis have not been fully clarified. Objective.—To investigate whether expressions of TGF-βs are related to myofibroblast distribution in chronic, cancer-associated, obstructive pancreatitis (COP). Design.—Histopathologic studies using hematoxylin-eosin and Elastica-Masson trichrome and immunohistochemical studies using antibodies against α-smooth muscle actin (SMA); CD68; TGF-β1, -β2, and -β3; and TGF-β soluble receptor type II were performed in 19 COP cases and 6 controls. By classifying COP tissues into 3 fibrosis phases by the amount of collagen deposits, immunoreactivities for TGF-βs, histopathologic changes, and myofibroblast distribution were examined for each fibrosis phase. Results.—Six cases were categorized in the early stag...