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.

We report a case of perivascular epithelioid cell tumor (PEComa) with an SFPQ/PSF-TFE3 gene fusion in a 14-year-old girl treated for adrenal neuroblastoma for 4 years. Imaging studies revealed a tumor in the wall of the sigmoid colon, which was radiologically different from the neuroblastoma, together with several inguinal and cervical lymph node metastases of the neuroblastoma. Microscopically, the tumor in the sigmoid colon showed sheet-like growth of epithelioid cells with abundant clear cytoplasm and round nuclei, which were separated by thin fibrovascular septa. These epithelioid cells were immunohistochemically positive for vimentin, gp100 (detected with monoclonal antibody HMB-45), and TFE3, and the tumor was diagnosed as PEComa. In a fluorescence in situ hybridization assay using an in-house probe for TFE3, the tumor cells showed split signals, indicating a rearrangement of TFE3. Molecular cloning using 5' rapid amplification of complementary DNA ends and subsequent reverse transcription-polymerase chain reaction revealed an SFPQ/PSF-TFE3 gene fusion. To the best of our knowledge, this is the second reported case of metachronous PEComa subsequent to a primary tumor, and the first report confirming an SFPQ/PSF-TFE3 gene fusion in PEComa.

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The authors report on a case of histiocytic sarcoma (HS) in a pediatric patient presenting with a solitary tumor in the cerebellum, with the aim of providing insight into primary HS in the CNS, which is especially rare. A 17-month-old Japanese girl presented with a 2-week history of progressive gait disturbance. Brain MRI revealed a 4.7 × 4.3 × 4.3–cm well-demarcated solitary mass in the right hemisphere of the cerebellum, initially suggestive of medulloblastoma, ependymoma, or anaplastic astrocytoma. On intraoperative inspection the cerebellar tumor showed intensive dural attachment and was subtotally removed. Histological and immunohistochemical findings were consistent with HS. The patient subsequently received chemotherapy, and her preoperative neurological symptoms improved. Primary HS in the CNS usually demonstrates an aggressive clinical course and is currently considered to have a poor prognosis. The possibility of this rare tumor should be included in the differential diagnosis of localized cerebellar tumors in the pediatric age group.

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