Membranous nephropathy is an immune disease in which immune complexes are deposited under the glomerular epithelium, damaging the filtration barrier and resulting in severe proteinuria.　Recently, a new technology called laser microdissection-liquid chromatography mass spectrometry （LMD-LCMS/MS） has been applied to pathological tissue sections, revealing the causative antigens of this disease.　As a result, many causative antigens, including phospholipase A2 receptor （PLA2R）, which is found in 70% of membranous nephropathy cases, have been identified as proteins expressed in glomerular podocytes.　Corresponding autoantibodies are detected in the blood, leading to the understanding that membranous nephropathy is an autoimmune disease targeting podocytes.　In addition, since the autoantibody subclass is IgG4, this disease can be considered an IgG4-related autoimmune disease.　Membranous nephropathy was previously classified as idiopathic or secondary, but with the identification of causative antigens, it is now classified based on the specific antigen involved.　The elucidation of the pathogenesis and selection of treatment strategies have begun based on the causative antigen and the characteristic IgG4 immune response in membranous nephropathy.

Telepathology using digital whole slide images is a practical challenge in the field of pathology.　Three initiatives of digital telepathology of Asahi General Hospital were presented, which included collaboration with a regional hospital for cancer treatment, support from a hospital branch clinic of pathology in Tokyo, and collaboration with another hospital using Class II devices.　These demonstrated that digital telepathology is a realistic means to resolve both issues, “shortage of pathologists in Japan” and “all pathology diagnosis at health care institutions.”　We should overcome six restriction rules in Japanese medical insurance systems for the promotion of digital telepathology, regarding to 1） network construction with hospitals and clinics, 2） diagnostic devices, 3） collaborative intraoperative diagnosis, 4） setup of pathology clinics, 5） 80%-specimen rule for commercial laboratory, and 6） criteria for full-time remote pathologists.　It is expected that many attempts of digital telepathology will be developed and shared in the near future.

Squamous cell carcinoma, which accounts for more than 90% of all malignant lesions in the oral cavity.　Although most cases are well-differentiated showing invasive growth forming nests with keratinization, there are rare histologic subtypes of squamous cell carcinoma that have unique histologic features.　Among these, carcinoma cuniculatum has been increasingly reported recently.　Although it shows marked endophytic growth, its prognosis seems to be better than conventional oral squamous cell carcinoma.　

The patient, a female in her 70s, presented with left lower abdominal pain and an elevated CRP level.　Endoscopy revealed multiple ulcers throughout the colorectum of unknown etiology.　When the early colon cancer in the ascending colon was resected, a novel amyloid-causing protein, epidermal growth factor-containing fibrin-like extracellular matrix protein 1 （EFEMP1） was identified in the colonic wall, leading to a diagnosis of AEFEMP1 amyloidosis.　Subsequently, the abdominal pain worsened and ulcers showed further progression especially in the colonic side of the ileocolonic anastomosis, descending and sigmoid colon.　Finally, the remaining colon was resected.　Histopathological examination of the surgical specimens of the colon revealed that EFEMP1-derived amyloid protein （AEFEMP1） deposits were present mainly in the venous walls from the submucosa to the serosa.　AEFEMP1 is an amyloid-causing protein newly added to the amyloid classification of the International Amyloidosis Society in 2020.　It is deposited throughout the body with aging, particularly in the venous walls of the colon, but it may be overlooked because it is weakly positive for Congo red staining.　In cases of intractable colonic ulcer in the elderly patients, evaluation of AEFEMP1 may help identify the underlying cause.

A metaplastic thymoma is a rare thymic neoplasm.　A 92-year-old woman underwent resection of an anterior mediastinal tumor.　Histopathological findings showed a biphasic pattern of polygonal epithelioid and spindle cells.　The epithelioid cells were characterized by cellular atypia, including enlarged nuclei, irregular nuclear shapes, and increased chromatin content.　The two cellular components showed areas of transition, and cellular atypia was also observed in some spindle cells.　Based on histopathological and immunohistochemical findings, the patient was diagnosed with metaplastic thymoma.　Although cellular atypia has been reported in metaplastic thymomas, it is usually confined to epithelioid cells, and cellular atypia in spindle cells is uncommon.　Metaplastic thymomas are rarely encountered in routine practice;therefore, pathologists should be familiar with the variability of their histologic features.

We report a case of myoepithelioma-like tumor of the vulvar region （MELTVR）.　A woman in her 60s had a 2cm subcutaneous tumor on the perineum.　Histologically, the tumor extended from the subcutaneous tissue to the dermis.　The tumor consisted of the proliferation of spindle-shaped and epithelioid cells with abundant myxoid stroma.　The histology resembled that of soft tissue myoepithelioma;however, immunohistochemically, AE1/AE3 showed very focal and weak positivity, CAM5.2, S-100, and GFAP were negative, and EWSR1 gene rearrangement was absent.　Additional immunohistochemical evaluation was performed, and the diagnosis of MELTVR was confirmed based on the expression of Estrogen receptor and complete loss of SMARCB1 expression.　The infiltrative proliferation into the dermis was a characteristic feature of this case.　In addition, we report on MELTVR from the perspective of tumors that show loss of SMARCB1 expression, along with a discussion of the literature.

We report a case of Mpox virus infection in 30s-year-old man.　He had sexual contact with a multiple sex partner one month ago.　He had a fever and skin rash （erythema, papules or pseudopustules） on his chest, forearms, palms, and penis.　Microscopic examination of the skin biopsied specimen from his chest revealed epidermal necrosis with shadow cells, balloon cell degeneration, and exocytosis of neutrophils.　Eosinophilic inclusion bodies were observed in keratinocytes.　A final diagnosis of Mpox virus infection was confirmed by PCR.　As the histopathological features are not specific for Mpox virus infection, it is necessary to interactively diagnose in combination with patient’s history and clinical findings.

We report a case of mixed neuroendocrine-non-neuroendocrine neoplasm （MiNEN） with squamoid morule.　A 44-year-old man presented with fresh blood hemorrhage in his stool.　Endoscopic examination revealed a colon tumor and the patient subsequently underwent right hemicolectomy.　Histologically, the tumor contained both adenocarcinoma and neuroendocrine tumor （NET G3） components with each component occupying more than 30% of the tumor.　Both components exhibited squamoid morule.　The patient was diagnosed with MiNEN with squamoid morule, which are rare.

Gliosarcoma is a rare and highly malignant central nervous system tumor, comprising approximately 2% of all glioblastomas and characterized by differentiation into both glial and mesenchymal components.　The clinical significance of distinguishing between glioblastoma and gliosarcoma lies in their differing prognoses, with gliosarcoma showing a median survival of 9 months compared to 15 months for glioblastoma.　This report presents a case of an elderly man diagnosed with gliosarcoma following the detection of limb muscle spasticity and the identification of a neoplastic lesion in the left cingulate gyrus via MRI.　The diagnosis was confirmed by identifying a biphasic pattern of glial and mesenchymal components.　Additionally, specific molecular abnormalities such as TP53 mutation, ATRX mutation, CDKN2A deletion, and PTEN deletion were identified.　These findings underscore the importance of integrating morphological features with molecular genetic testing to diagnose gliosarcoma accurately.

We report an instructive case of fibrin-associated large B-cell lymphoma （FA-LBCL） in the scrotum.　A male in his 80s noticed the enlargement of the right scrotum 25 years after the ipsilateral herniorrhaphy.　The resected scrotal tumor consisted of massive fibrin deposition.　There were a few large abnormal lymphocytes in the periphery, which express CD20, CD79a, PAX5, CD30, and EBER, leading to the diagnosis of FA-LBCL.　Despite its large-cell-morphology, FA-LBCL is slow-growing and curable with surgery alone.　It is important to precisely distinguish FA-LBCL from other types of LBCL.

The patient was a woman in her 7th decade who had a subcutaneous tumor in her lower abdomen.　Histologically, most of the tumor consisted of fibrosarcomatous dermatofibrosarcoma protuberans （DFSP）, with a small amount of typical DFSP at the margins.　In addition, nodules of spindle-shaped cells were characteristically scattered in the lesion.　Immunohistochemical staining revealed that the spindle-shaped cells in the nodules were αSMA-positive, CD34-negative and desmin-negative, resembling myofibroblasts, which led to the diagnosis of fibrosarcomatous DFSP with myoid differentiation.　Additionally, fluorescence in situ hybridization suggested the presence of the chromosomal translocation （COL1A1::PDGFB fusion） in both typical DFSP components and the myoid nodules.　Fibrosarcomatous DFSP with myoid differentiation is a rare histologic variant, and its diagnosis is difficult because it exhibits different morphologic and immunohistochemical profiles than classic DFSP, so gene fusion detection and careful observation of the entire lesion are recommended.

A patient, a male in his 70s, underwent endoscopic submucosal dissection （ESD） of gastric adenocarcinoma （pT1b, negative margin） at the previous hospital and an additional distal gastrectomy at our hospital.　One year later, a liver tumor was detected, resected, and found to be adenocarcinoma.　To determine whether the tumor was primary intrahepatic cholangiocarcinoma or metastatic gastric adenocarcinoma, we reviewed the ESD specimens from the previous hospital. Both showed clear cytoplasm and were positive for spalt-like transcription factor-4 （SALL4）.　Hence, the diagnosis was made that the primary gastric enteroblastic adenocarcinoma had metastasized to the liver.　Gastric enteroblastic adenocarcinoma is a histological subtype with a poor prognosis, and when its characteristic histology is observed, immunohistochemistry for SALL4 or other markers should be performed and the information should be conveyed to clinicians.