Von Recklinghausen's disease usually runs a benign course, punctuated frequently by exacerbations produced by puberty, pregnancy, menopause, trauma, and infection. In some cases the tumors become stationary, but, on the other hand, sarcomatous change may take place in from 6.6% to 16% of patients, according to various authors. Most of the reported cases of malignancy have occurred in the third, fourth, and fifth decades of life and have had an approximately equal sex distribution. No definite relationship seems to exist between the occurrence of sarcoma and the number of cutaneous lesions. The malignant changes have a predilection for the deep nerves of the extremities and face, but cases of neurofibrosarcoma have been reported as originating in the mediastinum, retroperitoneal space, and along the gastrointestinal tract. In a very few patients, simultaneous malignant transformation has occurred in several tumors.
Clinically, the neurofibrosarcomas arising in