Histopathologic Evaluation of Atypical Neurofibromatous Tumors and Their Transformation into Malignant Peripheral Nerve Sheath Tumor in Neurofibromatosis 1 Patients - A Consensus Overview (original) (raw)

Neurofibromatosis 1 (NF1) patients develop multiple neurofibromas, with 8-15% of patients experiencing malignant peripheral nerve sheath tumor (MPNST) during their lifetime. Prediction of transformation, typically from plexiform neurofibroma, is clinically and histologically challenging. In this overview, following a consensus meeting in October 2016, we outline the histopathologic features and molecular mechanisms involved in the malignant trans-formation of neurofibromas. Nuclear atypia alone is generally insignificant. However, with atypia, loss of neurofibroma architecture, high cellularity, and/or mitotic activity >1/50 but <3/10 high power fields, the findings are worrisome for malignancy. We propose the term "atypical neurofibromatous neoplasms of uncertain biologic potential (ANNUBP)" for lesions displaying at least two of these features. This diagnosis should prompt additional sampling, clinical correlation, and possibly, expert pathology consultation. Curre...