Plexiform neurofibroma with and without associated malignant peripheral nerve sheath tumor: a clinicopathologic and immunohistochemical analysis of 54 cases.

Plexiform neurofibroma (PNF) is an important part of the diagnostic criteria for neurofibromatosis type 1 (NF1) and is a known precursor lesion of malignant peripheral nerve sheath tumor (MPNST). We studied the clinicopathologic features of 54 cases of PNF for which the hematoxylin- and eosin-stained slides and paraffin blocks were available and adequate clinical follow-up could be obtained. In addition, in all cases, a representative section of the PNF and, when present, MPNST, was evaluated immunohistochemically with an antibody for p53 (DO7). The cohort included 28 male patients and 26 female patients, with an age range from 4 to 79 years (mean, 27 yr). Of these 54 patients, 46 (85%) met the strict diagnostic criteria for NF1. Thirty-nine patients had PNF alone; 15 patients had an MPNST arising from the PNF (PNF/MPNST). Those patients with PNF/MPNST tended to be older (38 yr vs. 22 yr) and to have larger tumors (10.5 cm mean vs. 7.4 cm mean) than those with PNF alone. In 9 patients (23%) of 39 with PNF alone, local recurrence developed, whereas in 7 patients (47%) of 15 with PNF/MPNST, recurrent MPNST developed, and metastases developed in 3 (20%) of the 15. Immunohistochemically, only 1 case (2.5%) of 39 cases of PNF alone stained for p53. On the other hand, 12 (80%) of 15 cases of PNF/MPNST showed p53 immunoreactivity in the MPNST component, 2 of which also showed staining in the PNF areas. In conclusion, we found that the vast majority of patients with PNF met the strict diagnostic criteria for NF1. The immunohistochemical detection of intranuclear p53 protein is common in the malignant areas of PNF/MPNST but is rare in the PNF regions. The rarity of p53 staining in the PNF regions precludes its use in predicting those tumors that are likely to progress to MPNST.