This case shows packed
marrow with large plasmablastic/immunoblastic cells
Neoplastic plasma cells may show a variety of morphologic
features, including mature, intermediate, immature, and
plasmablastic features. Some myeloma cells may even be
lymphoid-appearing. Plasma cell myeloma infiltration in the marrow
can be very focal and subtle, and occasionally it is almost
impossible to appreciate the tumor with clot/trephine biopsy only.
Therefore, it is probably worthwhile to perform CD138 immunostain
if no apparent plasma cells are noted in the marrow
Also, solitary plasmacytoma may present at the extramarrow
sites without typical clinical presentations or marrow
involvement; occasionally, the tumor cells may not be plasma
cell-appearing at all, which can resemble poorly differentiated
carcinoma, sarcoma, melanoma or lymphoma. Therefore, plasmacytoma
should be considered as one of the differential diagnoses when
facing a wired tumor of unknown origin