OBJECTIVETo investigate the architectural and cytological variations of plasma cell neoplasms, and discuss the diagnosis and differential diagnosis.

METHODSHistological and immunohistochemical examinations were used to study the morphologic and immunophenotypic features of 46 cases of plasma cell neoplasms.

RESULTS40 out of 46 cases were diffuse growth pattern. 3 cases had a nestlike architecture that can mimic neuroendocrine tumors and 3 cases had a prominent fibrous sclerosis background. Amyloid deposition, calcification or ossification and angiomatoid areas can be prominent and may obscure the neoplastic plasma cells. Cytologically, 30 cases were composed of relatively mature plasma cells and can be recognized without too much difficulty. Tumor cells resembled immunoblasts in 6 cases and small lymphocytes in 4 cases. In another 2 cases tumor cells were easily confused with Signet-ring cells or clear cells. Tumor cells were composed of anaplastic cells, histocytoid cells and spindle cells in each one case, respectively. Lastly, tumor cells can be polymorphous which composed of multilobated, monocytoid or multinucleated cells in one case. 93.1% (27/29) cases expressed CD79a while only 5.1% (2/39) cases expressed CD20.87.1% (27/31) cases expressed CD38 and 83.3% (25/30) cases expressed CD138, 96.8% (30/31) cases expressed MUM-1. Light chain restrictions were detected in 38 cases, that 27 cases expressed lambda and 11 for kappa.

CONCLUSIONSExcept for the common architecture and cytology in plasma cell tumor, unusual morphology may appear. Thus, pay attention to distinguish from lymphoma such as small lymphocytic lymphoma and anaplastic large cell lymphoma, pooly differentiated carcinoma, clear cell carcinoma or Signet-ring cell carcinoma, sarcoma, etc. And immunohistochemistry is essential in the diagonosis.