Enrico Martin

16 Chapter 1 impair oncological outcome in STS. Even so, its application and safety in MPNST is not entirely clear as guidelines simply recommend performing complete and wide resections to achieve R0 margins. The resection of nerves is likely to be inevitable in many cases, but functional reconstructions may still be possible. Such reconstructions include the reconstructions of tendon, muscle, and nerve function and are increasingly being employed in trauma cases, yet are not standard of care in any STS. 43,44 Nerve reconstructions provide the opportunity to not only regain motor function, but also restore lost sensation. Moberg already proposed in the ‘50s that an insensate hand as good is as a non-functional hand. 45 Table 3 Pathological definitions of transitional states between neurofibroma, low-grade MPNST and high-grade MPNST. Diagnosis Pathological definition a Neurofibroma Benign Schwann cell tumor with thin, wavy nuclei, wispy cell processes, and myxoid to collagenous matrix. Immunohistochemistry includes extensive but not diffuse positivity of S100 and SOX10 and a lattice-like CD34 positive fibroblastic network. Plexiform neurofibroma A neurofibroma which is diffusely enlarging and replacing a nerve, commonly including multiple nerve fascicles. It is delineated by EMA positive perineurial cells. Neurofibroma with atypia Neurofibroma with only atypia, generally manifesting as scattered bizarre nuclei Cellular neurofibroma Neurofibroma with hypercellularity, but retained neurofibroma architecture and <1 mitosis per 50 HPF ANNUBP Schwann cell tumor with at least 2 of 4 features: cytologic atypia, loss of neurofibroma architecture, hypercellularity, >1 mitosis per 50 HPF and <3 mitoses per 10 HPF Low-grade MPNST ANNUBP feature, but with 3-9 mitoses per 10 HPF and no necrosis High-grade MPNST MPNST with at least 10 mitoses per 10 HPF or 3-9 mitoses per 10 HPF combined with necrosis. a : classification adapted from Mietinnen et al. 2017 29 , ANNUBP: atypical neurofibromatous neoplasm of uncertain biologic potential, HPF: high-power field, MPNST: malignant peripheral nerve sheath tumor