How can plasma cell tumors be characterized?

Plasma cell tumors are characterized primarily by the presence of numerous plasma cells, which exhibit distinct morphological features. One of the key characteristics is that these cells often possess eccentrically located nuclei, meaning the nuclei are not centered within the cell but rather pushed to one side. Additionally, plasma cells typically have a perinuclear halo—a clear zone surrounding the nucleus that is due to the abundant rough endoplasmic reticulum necessary for immunoglobulin production.

The presence of eccentrically located nuclei and clear zones is essential in distinguishing plasma cells from other types of hematological malignancies or normal lymphoid cells. The eccentrically positioned nuclei reflect the functional adaptations of plasma cells, which are actively producing antibodies, hence highlighting their identity as plasma cells within tumor samples.

The other characteristics mentioned do not align with how plasma cell tumors are identified histologically. Notably, prominent granules are more characteristic of different cell types, such as granulocytes. Uniformly sized round cells do not represent the diversity seen in plasma cell morphology, and cells clustered in sheets may indicate other types of tumors or cellular formations common in various malignancies, which are not specific to plasma cells.