Nasopharyngeal alveolar rhabdomyosarcoma expressing CD56: a mimicker of extranodal natural killer/T-cell lymphoma.

Alveolar rhabdomyosarcoma (ARMS) is remarkably rare in adults older than 45 years. Histologically, the tumor is composed of blue round cells with frequent expression of CD56 in addition to myogenic markers. Recent studies of ARMS have shown two specific recurrent translocations: PAX3-FKHR [t(2;13)(q35;q14)] or PAX7-FKHR [t(1;13)(p36;q14)]. Extranodal natural killer (NK)/T-cell lymphoma (ENKTL) occurs most frequently in the upper aerodigestive tract with a male preference in East Asia and Central and South Americas with neoplastic cells frequently expressing CD56. We report a 53-year-old Taiwanese man presenting with a nasopharyngeal mass, cervical lymphadenopathy, and multiple bone metastases. Histologically, the nasopharyngeal biopsy revealed diffuse sheets of small blue round tumor cells without obvious alveolar pattern, angioinvasion or tumor necrosis. An initial erroneous diagnosis of ENKTL was made due to CD56 expression using fresh tumor tissue with flow cytometric analysis and the patient was treated accordingly. Retrospective study showed that the tumor cells expressed CD56, desmin, and myogenin. Fluorescence in situ hybridization revealed that the tumor cells were positive for FKHR gene rearrangement, confirming the diagnosis of ARMS. Our case illustrates that a diagnosis of ENKTL based solely on CD56 expression can be misleading for a nasopharyngeal small blue round cell tumor. ARMS should be included as a differential diagnosis, and a correct diagnosis can be reached only after a high index of suspicion and a thorough histological examination with the aid of ancillary studies.

Mycobacterium abscessus granulomatous prostatitis.

Infectious granulomatous prostatitis is uncommon, and most cases of granulomatous prostatitis are classified as nonspecific granulomatous prostatitis. From 2007 to 2009, 5 patients experienced poor wound healing after radical prostatectomy for prostate cancer at a specialist cancer center. Mycobacterium abscessus was cultured from the debridement specimens, and acid-fast-positive bacilli were identified histologically within the prostates. All 180 radical prostatectomy specimens from May 2007 to June 2009 were reviewed, and 7 additional cases with morphologies suspicious of M. abscessus granulomatous prostatitis (MAGP) were identified. The characteristic morphologic feature of MAGP was suppurative necrotizing granulomatous inflammation extensively (10% to 80% of the gland; mean, 39%) involving the prostate. The centers of MAGP were large areas of neutrophilic abscess and necrotic debris, which were surrounded by histiocytes, lymphocytes, plasma cells, scattered multinucleated giant cells, and eosinophils. In the adjacent areas, there was a lobular extension of mixed inflammatory infiltrates into dilated and ruptured ducts. Involvement of extraprostatic soft tissue and seminal vesicles/vas deferens was found in 9 and 4 cases, respectively. Acid-fast-positive bacilli were identified in 5 radical prostatectomies. Eleven patients had fresh tissue specimens stored at -150°C, and M. abscessus was cultured from 8 prostates. Random amplified polymorphic DNA-polymerase chain reaction showed the same clone for all isolates. After prostatectomy, 8 patients experienced prolonged wound healing, with urethrorectal fistula formation in 1 patient and a pelvic abscess in another. It is critical for pathologists to recognize MAGP and to distinguish it from the more common nonspecific granulomatous prostatitis and other granulomatous lesions within the prostate.