Abstract: Objective To investigate the clinicopathologic characteristics of atypical neurofibromatous neoplasm of uncertain biologic potential （ANNUBP） for improving the diagnosis of the disease. Methods One case of ANNUBP was observed and studied for its clinical symptoms, imaging features, pathological characteristics and immunohistochemical phenotypes of surgical specimens, and also relevant literature was reviewed. Results The middle-aged female patient was found a mass on her right hip more than 1 year ago; MRI examination showed that there were patchy abnormal signal shadows, low signal on T1WI, and high signal on T2WI. The lesion area was about 10.2 cm×7.8 cm×7.2 cm. Microscopically, the tumor cells showed atypially and the cell density increased significantly, with the absence of structural characteristics of neurofibroma and visible mitosis. Immunohistochemistry showed positive staining of S-100, SOX10, H3K27me, and a small amount positive of P16. Conclusion ANNUBP is a kind of malignant precursors or early changes of malignant lesions, and the risk of progressing to malignancy increases obviously. Some parts of the lesions are not easy to be completely removed and local recurrence may occur but not metastasis.

Key words: Atypical neurofibromatous neoplasm of uncertain biologic potential, Diagnosis, Differential diagnosis