Primitive neuroectodermal tumor as a differential diagnosis of CD56-positive tumors in adults.

A 33-year-old Japanese man was referred to our hospital after a huge intrapelvic tumor with bilateral hydronephrosis was found following persistent lumbago. Natural killer/T-cell lymphoma was suspected due to positive immunostaining for CD56, but CHOP therapy was ineffective. Re-evaluation of the tumor cells showed that they were positive for CD99, neuron-specific enolase, and synaptophysin and had a t(11 ; 22) (q24 ; q12) translocation, leading to the revised diagnosis of primitive neuroectodermal tumor (PNET). Systemic chemotherapies and radiation therapy were added to surgical resection, and no recurrence has been detected for 3 years. Taken together, PNET may be considered in adult patients with CD56-positive tumors.