Unusual coexistence of extramedullary plasmacytoma and nasopharyngeal carcinoma in nasopharynx

Nasopharyngeal carcinoma (NPC) is an EBV-associated malignant tumor of nasopharynx. As extremely rare condition, the second primary cancer of nasopharynx can occur in NPC patients synchronously or subsequently. Extramedullary plasmacytoma (EMP) is a rare tumor and commonly originates in the head and neck region. However, there is no report to describe a collision tumor of NPC and EMP occurring in the same nasopharyngeal mass. We report here an unusual case of synchronous coexistence of NPC and EMP occurring in the nasopharynx of an old male patient. A 63-year-old male patient presented with a 3-month history of right-sided nasal obstruction and recently intermittent epistaxis without enlargement of cervical lymph nodes. The solitary mass of nasopharynx was found by radiological and nasopharyngeal examination. Histologically, the mass contained two separated portions and displayed typically histological features of NPC and EMP, respectively. In EMP portion, the tumor was composed of monomorphic plasmacytoid-appearing cells with immuno-positive to CD79a, CD138, CD38, MUM-1 and CD56, but lack immunoreactivity to pan-CK (AE1/AE3), CD20, CD21 and EBERs. In NPC portion, the tumor cells formed irregular-shaped islands with diffusely immuno-positive to pan-CK (AE1/AE3), EMA and EBERs, but lack expressions of lymphoplasmacytic markers. A diagnosis of simultaneous occurrence of EMP and NPC in nasopharynx was made. There was no evidence of tumor recurrence or metastasis 18-month follow-up after radiotherapy. To our knowledge, it may be the first case of coexistence of EMP and NPC synchronously. In addition, the histological differential diagnosis and relevant potential mechanism of this unusual collision tumor were also discussed.