Histopathology and clinical outcome of NF1-associated vs. sporadic malignant peripheral nerve sheath tumors.

The differences in the clinical course and histopathology of sporadic and neurofibromatosis type 1 (NF1)-associated malignant peripheral nerve sheath tumors (MPNST) were investigated retrospectively. The collective comprised 38 NF1 patients and 14 sporadic patients. NF1 patients were significantly younger at diagnosis (p<0.001) and had a significantly shorter survival time than sporadic patients (median survival 17 months vs. 42 months, Breslow p<0.05). The time interval to local recurrence and metastatic spread was also significantly shorter in NF1 patients (9.4 months vs. 30.0 months, p<0.01; 9.1 months vs. 33.2 months, p<0.001, respectively). In patients with the original histopathological data available (22 NF1 patients, 14 sporadic cases), NF1-associated MPNST showed a significantly higher cellularity compared to sporadic tumors (p<0.001) whereas sporadic MPNST featured a significantly higher pleomorphism (p<0.01). Most importantly, while histopathological variables correlated with French Fédération Nationale des Centres de Lutte Contre le Cancer grading in sporadic MPNST, this was not the case for NF1-associated tumors. The differences between NF1-associated and sporadic MPNST in regard to the clinical course and histopathology may reflect some fundamental differences in biology and pathomechanism of the two tumor groups. Our findings indicate the necessity for a separate grading scheme which takes into account the genetic background in NF1 patients.