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Background: Lymphatic malformations (LMs) are congenital low-flow vascular anomalies resulting from abnormal embryogenesis. Clinical researches have shown that rapamycin, a specific inhibitor of mTOR, is effective in treating LMs. It suggests the abnormality of mTOR signal pathway in LMs. Methods and Results: From January 2009 to December 2018, 10 patients who accepted the resection of LMs were enrolled into the study. Samples of each subtype of LMs (macrocystic, microcystic, and mixed subtypes) were further investigated. Expression of molecules in mTOR signal pathway-mTORC1, p70 S6, p-p70 S6, elF4EBP1, and p-elF4EBP1-in LMs were investigated by immunohistochemical staining. Location of mTORC1, p70 S6, and elF4EBP1 in LMs were shown by immunofluorescence co-staining. Phosphorylation level of mTOR signal pathway in LMs was examined by Western blotting. Immunohistochemical staining showed the expression of mTORC1, p70 S6, p-p70 S6, eIF4EBP1, and p-eIF4EBP1 in LMs. Immunofluorescence staining further verified the co-expression of mTORC1, p70 S6, and eIF4EBP1 in the lymphatic endothelium of LMs. Western blotting analysis revealed obviously higher phosphorylation level of mTOR signal pathway in LMs than that in normal skins ( P  < 0.05). Conclusions: The results showed that the mTOR signal pathway was overactivated in LMs. The study provides compelling evidence for treating LMs or syndromes with lymphatic anomalies by inhibiting mTOR signaling.

Background: Extensive lymphatic malformations are low-flow vascular malformations that can cause devastating complications. Treatment of these malformations is challenging. This systematic review presents current use of sirolimus in patients with extensive lymphatic malformations., Methods: MEDLINE and Google scholar search was conducted for studies on sirolimus treatment of lymphatic malformations up to July 2017. Search items included "lymphatic malformation," "lymphangioma," "cystic hygroma," "vascular malformation," "low-flow malformation," "sirolimus," "rapamycin," and "mTOR inhibitor.", Results: Twenty studies, including 71 patients receiving sirolimus, were included into this review. Forty-five patients had lymphatic malformations, eight patients venolymphatic malformations, and 19 patients capillary-lymphatico-venous malformations. Sirolimus led to a partial remission of disease in 60 patients, three patients had a progressive disease, and the outcome of eight patients was not reported. Dosing, target trough level, and duration of treatment differed between the studies. Common adverse effects were hyperlipidemia and neutropenia., Conclusions: Available literature indicated that sirolimus therapy might be effective for lymphatic malformations. However, further randomized controlled studies are required to analyze the efficacy and long-term adverse events and to clarify the potential role for sirolimus in the management of lymphatic malformations.

Background: Lymphatic endothelial cells (LECs) derived from lymphatic malformations (LMs) bear activated PIK3CA alleles yet display an inflammatory gene expression profile. A basis for the inflammatory phenotype was sought by screening for coexisting somatic mutations., Methods and Results: Fourteen independent LEC populations bearing activated PIK3CA alleles were isolated from LM. These were characterized by the expression of growth and inflammatory genes (VEGFC, IL-6, COX-2, IL-8, HO-1, E-SEL) by qRT-PCR. Most commonly upregulated gene products were VEGFC, COX2, HO-1, and ANGPTL4. The specific inhibition of PI3K reduced VEGFC expression without resolving inflammation. Whole exome sequencing of six LM-LEC populations identified five novel somatically acquired alleles coexisting with activated PIK3CA alleles. Two affected genes regulate lipid droplet metabolism (FITM2 and ATG2A), two are gene regulators (MTA1 and TAF1L), and the fifth is an isoform of ANK3 (an endosomal/lysosomal protein). Inhibition of AMPK implicated its involvement in regulating COX-2 and HO-1 overexpression. ANGPTL4 expression was independent of AMPK and PI3K activity and reflected lipid stress demonstrated in normal LECs. AMPK activation with AICAR had a selective growth-limiting effect in a subset of LM-LEC isolates., Conclusions: Inflammatory stress displayed by LM-LECs is consistent with errors in lipid metabolism that may be linked to acquired mutations. The acquisition of PIK3CA alleles may be a permissive event that antagonizes inflammation and metabolic defect.