Pathologists use plasmacytoid to describe cells that look like plasma cells. Plasma cells are immune cells that make antibodies. They have a round or oval shape, a generous amount of cytoplasm, and a nucleus that sits off to one side of the cell rather than in the center.
Plasmacytoid is a description of what the pathologist saw under the microscope, not a diagnosis on its own. Many different cell types can take on a plasmacytoid appearance, in both noncancerous and cancerous tumors. This article explains what plasmacytoid cells look like, where they are found, and what the term means in your pathology report, including the plasmacytoid subtype of urothelial carcinoma.
Plasmacytoid cells are usually round or oval and are often found as single cells or in loose groups. The nucleus is pushed to one edge of the cell, which pathologists describe as “eccentric.” The rest of the cell is filled with cytoplasm, which often looks pink or purple on routine slides.
Despite their appearance, most plasmacytoid cells are not plasma cells. The word describes only their shape. The pathologist uses the location of the tumor, the other cells around them, and additional tests to work out what the cells really are.
Plasmacytoid cells can be seen in many tumor types. Common examples include:
Because the same appearance occurs in so many different tumors, the word plasmacytoid does not tell you on its own whether a tumor is noncancerous or cancerous. Your report will list the final diagnosis separately.
Plasmacytoid cells can come from many different cell types, so pathologists often use immunohistochemistry to identify them. This test uses antibodies to detect proteins made by particular cell types. The pathologist chooses a group of markers, called a panel, based on the diagnoses being considered.
For example, true plasma cells are positive for CD138. Melanoma cells are positive for melanoma markers, and carcinoma cells are positive for epithelial cell markers. Some markers can be misleading on their own. Plasmacytoid urothelial carcinoma, for instance, is often positive for CD138, the same marker used to identify plasma cells. For this reason, no single marker is used alone, and the results are interpreted together with the appearance of the tumor.
Plasmacytoid urothelial carcinoma is a rare type of bladder cancer in which many of the cancer cells look like plasma cells. It is a subtype of urothelial carcinoma, the most common type of bladder cancer. Older reports may call it the “plasmacytoid variant.” The World Health Organization classification of urinary tract tumors, published in 2022, changed the term from “variant” to “subtype.”
Cells in plasmacytoid urothelial carcinoma usually spread through tissue as single cells rather than in solid groups. This happens because most of these tumors have lost a protein called E-cadherin, which normally helps cells stick together. As a result, cells can spread along the layers of the bladder wall and into the lining of the abdomen.
Plasmacytoid urothelial carcinoma is often found at a more advanced stage than the usual type of urothelial carcinoma. It tends to grow and spread more quickly, and it is more likely to come back after treatment. For these reasons, your report may say how much of the tumor is made up of the plasmacytoid subtype. Your care team considers this information when planning treatment.