Neoadjuvant Everolimus for Adult Giant Mesenteric Cystic Lymphangioma with mTOR Pathway Activation.

Cystic lymphangioma are rare benign vascular or lymphatic tumors, diagnosed mostly in newborns or children, that may become life-threatening because of local invasiveness. Surgical "en-bloc" resection with negative margins is the only curative treatment, but some patients are diagnosed with unresectable tumors. We describe the case of a young adult with giant unresectable mesenteric lymphangioma. Extensive pathological characterization as well as whole exome and transcriptome sequencing enabled us to identify mTOR pathway activation within endothelial tumor cells. The patient was treated with everolimus and experienced major partial response, leading to the surgical resection of the residual lesions. This case highlights the importance of molecular characterization of adult cystic lymphangioma for mTOR pathway activation because multidisciplinary therapeutic approaches, including neoadjuvant everolimus and secondary surgery, can lead to complete cure of this rare condition. KEY POINTS: The case of an adult patient diagnosed with giant unresectable mesenteric cystic lymphangioma, in which activation of the mTOR pathway was documented at both the pathological and transcriptomic levels, is reported. This patient showed major partial response to the mTOR inhibitor everolimus, which led to the successful resection of residual tumor lesions after 9 months of treatment. This report shows that mTOR targeting should be considered as neoadjuvant treatment in adult large cystic lymphangioma, as it can lead to complete surgery and cure of this rare condition.