**Question:** Plasmacytoid lymphomas may be associated with an increase in

A. CD20
B. CD56
C. CD38
D. CD138

**Correct Answer:** D. CD138

**Core Concept:** Plasmacytoid lymphomas are a subtype of non-Hodgkin's lymphomas that exhibit plasma cell differentiation. These tumors are characterized by the abnormal proliferation of plasma cells, which produce monoclonal immunoglobulins.

**Why the Correct Answer is Right:** Plasmacytoid lymphomas are associated with an increase in CD138 expression. CD138, also known as syndecan-1, is a cell surface glycoprotein that is primarily expressed on mature plasma cells. In normal physiological conditions, CD138 is involved in the regulation of cell adhesion, migration, and differentiation of plasma cells. In plasmacytoid lymphomas, the overexpression of CD138 contributes to the neoplastic proliferation and secretion of monoclonal immunoglobulins.

**Why Each Wrong Option is Incorrect:**

A. CD20: CD20 is a B-cell specific surface antigen that is expressed on normal mature B cells, pre-B cells, and activated T cells. Although CD20 is downregulated or absent in some lymphomas, it is not typically overexpressed in plasmacytoid lymphomas.

B. CD56: CD56, also known as NKp46, is a molecule expressed on natural killer (NK) cells, subsets of T cells, and some subtypes of B cells. CD56 is not a specific marker for plasmacytoid lymphomas and does not correlate with the proliferation of plasma cells.

C. CD38: CD38 is a multifunctional glycoprotein expressed on various cell types, including lymphocytes, monocytes, and endothelial cells. While CD38 is overexpressed in some lymphoid malignancies, it is not specifically associated with plasmacytoid lymphomas.

**Clinical Pearl:**

Plasmacytoid lymphomas are a rare and aggressive lymphoproliferative disorder characterized by the clonal proliferation of plasma cells. Overexpression of CD138, as seen in option D, is a key feature of plasmacytoid lymphomas and is associated with the neoplastic proliferation of plasma cells. This information is crucial for identifying and differentiating plasmacytoid lymphomas from other lymphoproliferative disorders, such as monoclonal gammopathies, multiple myeloma, and plasma cell leukemia, which may also express CD138. Understanding the differential diagnosis is essential for appropriate diagnosis, treatment, and management of these patients.