**Question:** Maltoma is positive for-

A. CD20
B. CD5
C. CD3
D. CD19

**Correct Answer:** D. CD19

**Core Concept:** Maltoma is a term used to describe a type of non-Hodgkin lymphoma, a malignant proliferation of B cells. In this context, Maltoma refers specifically to mucosa-associated lymphoid tissue (MALT) lymphoma. B cells express various cell surface markers (antigens) that can be detected using monoclonal antibodies labeled with fluorochromes, allowing for identification and characterization of the tumor cells.

**Why the Correct Answer is Right:** CD19 is a cell surface marker expressed on the majority of B cells, including those in MALT lymphomas. In contrast, CD20 is typically downregulated or absent in these lymphomas, CD5 is expressed on a subset of B cell malignancies but not specifically on MALT lymphomas, and CD3 is a marker for T cells and does not apply in this context.

**Why Each Wrong Option is Incorrect:**

A. CD20: CD20 is typically downregulated or absent in MALT lymphomas, making it an incorrect choice.
B. CD5: CD5 is expressed on a subset of B cell malignancies but not specifically on MALT lymphomas, making it an incorrect choice.
C. CD3: CD3 is a marker for T cells and does not apply in this context, making it an incorrect choice.

**Clinical Pearl:** A positive CD19 staining is highly suggestive of a B cell origin in lymphoproliferative disorders and can be useful in distinguishing between MALT lymphomas and other B cell lymphomas. However, a negative or weak staining for CD19 does not exclude the diagnosis of MALT lymphoma. The diagnosis should be based on the clinical, morphological, and immunophenotypic features, along with the presence of a clonal B-cell rearrangement, and possibly, molecular genetic studies.

**Explanation of Maltoma and CD19 staining:**

Maltoma is a term used to describe a type of non-Hodgkin lymphoma originating from B cells found in mucosal-associated lymphoid tissue (MALT). CD19 is a cell surface protein expressed on the majority of B cells, including those in MALT lymphomas. CD19 staining can be used as a supportive tool to confirm the B cell origin of lymphoproliferative disorders.

**Core Concept:**

MALT lymphomas can present in various organs, such as the stomach, lung, salivary glands, and the conjunctiva. CD19 staining can help distinguish between MALT lymphomas and other B cell lymphomas, especially when the morphological and immunophenotypic features are ambiguous.

**Why CD19 staining is important:**

CD19 staining is particularly useful when the diagnosis is based on the clinical, morphological, and immunophenotypic features. Molecular genetic studies may also be performed to confirm the diagnosis of MALT lymphoma. However, CD19 staining provides a supportive tool to confirm the B cell origin of lymphop