OBJECTIVETo investigate clinicopathologic features of solitary plasmacytoma of bone (SPB) and the role of immuno-phenotype and immunoglobulin gene rearrangement detection in the diagnosis and differential diagnosis of SPB.

METHODSA total of 21 cases of SPB were selected during a period from 1990 to 2008. A retrospective clinicopathologic study and immunohistochemistry (EnVision or EliVision methods) of 17 antigens were performed. In addition, universal IgH (FR3A/LJH/VLJH) primers and BIOMED-2 PCR multiplex tubes were used for IgK and IgL rearrangement analysis.

RESULTSThe age of patients ranged from 36 to 72 years with a media of 50 years. Axial skeleton was the most common site of involvement, accounting for 66.7% of the cases (14 of 21), followed by the extremities of 33.3% (7 cases). Low serum level of M-components was found in 5 cases, including two of IgG type (21.4 g/L) and three of IgA type. Clinical manifestations were closely related to the anatomic sites involved, such as pain due to bone destruction, symptoms and signs caused by compression of spinal cord or nerve root, and pathological fracture. All cases presented as a solitary osteolytic lesion. According to the histological grading criteria, grade I tumor was seen in 12 of 21 cases (57.1%). The remaining were grade II (5 cases, 23.8%) and grade III (4 cases, 19.0%). Immunohistochemically, the neoplastic cells expressed two or more plasma cell antigens, including CD138, CD38 and PC, but no CD19 and CD20. CD79a expression detected in 23.8%(5/21) of the cases. Expression of CD56, CD27 and CD44v6 were 57.1% (12/21), 15.0% (3/20) and 23.8% (5/21), respectively. Follow-up data were available in 12 of the 21 patients (57.1%). Five patients were alive and 7 died. Three patients developed multiple myeloma (MM) and died of the tumor.

CONCLUSIONSSPB is a rare tumor with bone pain as the most common presenting symptom due to bone destruction. The diagnosis of EMP can only be established after exclusion of an extramedullay invasion by MM. Immunophenotype and IgH gene rearrangement analysis play important roles in the diagnosis of SPB.