Four Japanese cases of dendritic cell neurofibroma with pseudorosettes.

Dendritic cell neurofibroma with pseudorosettes (DCNWPR) is a rare peripheral nerve sheath tumor (PNST). To our knowledge, the only reported case of DCNWPR in Japan was documented by our team. We experienced three additional cases of DCNWPR in our institute since 2007, and report the clinical and histological features of DCNWPR of these Japanese cases. All four patients were adult women, with ages ranging 48-77 years (mean, 63.8). All patients presented with small solitary lesions that were clinically diagnosed as fibroma, melanocytic nevus or mixed tumor of the skin. Three cases were located on the back, and one on the cheek. Histopathologically, well-circumscribed nodules were present in the dermis, and composed of small lymphocyte-like cells with dark nuclei (type I cells) and larger cells with pale vesicular nuclei and abundant eosinophilic cytoplasm (type II cells). Small type I cells were grouped concentrically around the larger type II cells, thereby forming pseudorosettes. Immunohistochemical studies using antibodies against CD57 and S100 protein revealed that type II cells contained a copious cytoplasm endowed with a network of slender dendritic extensions. CD57 should be a useful marker for identifying type II cells because it allows these cells to be stained exclusively. We should recognize DCNWPR with its characteristic histological features such as pseudorosettes and presence of dendritic type II cells as a variant of PNST.