Malignant glomus tumor of the ileum mimicking GIST with distant metastasis without BRAF V600E mutation.

Glomus tumors arising in the gastrointestinal tract are rare and generally benign mesenchymal neoplasms that account for approximately 1% of all gastrointestinal soft tissue tumors. We report a unique case of malignant glomus tumor arising in the ileum of an elderly Chinese woman with widespread metastasis. The patient underwent local tumor resection for a presumed gastrointestinal stromal tumor (GIST). However, brain metastasis developed 2 years later, followed by a lesion in colon 6 months later and a subcutaneous mass of abdominal wall 12 months later. Then, local resections of all metastatic tumors were performed. Histopathology and immunohistochemical findings supported the diagnosis of malignant glomus tumor. Microscopic examination revealed that the primary and metastatic tumor cells shared common features: oval to spindle-shaped, with sharply defined cell membranes, round uniform nuclei, atypical mitotic figures, and variable necrosis. Immunohistochemical staining revealed positive expression of vimentin, SMA, caldesmon, MLH1, MSH2, MSH6, PMS2, SDHB and P53. Even with distant metastasis, the patient has been followed up for 28 months after the third operation without any radiotherapy and chemotherapy. To the best of our knowledge, this is the first report of a malignant glomus tumor arising from the ileum that metastasizes to the brain and abdominal wall with relatively favorable prognosis.