## **Core Concept**
Maltoma, also known as MALT (Mucosa-Associated Lymphoid Tissue) lymphoma, is a type of non-Hodgkin lymphoma that originates from the B cells in the MALT. The MALT is a part of the immune system found in various sites, including the stomach, small intestine, salivary glands, thyroid, lungs, and eye. The diagnosis and characterization of MALT lymphoma often involve specific immunohistochemical markers.

## **Why the Correct Answer is Right**
The correct answer, , is positive for CD20. CD20 is a membrane-embedded surface molecule which plays a role in the development and differentiation of B-cells into plasma cells. It is a specific marker for B cells and is used in the diagnosis of B cell lymphomas, including MALT lymphoma. MALT lymphomas are typically CD20 positive, which helps in their identification and in guiding therapy, as CD20 positive lymphomas can be targeted with rituximab, a monoclonal antibody against CD20.

## **Why Each Wrong Option is Incorrect**
- **Option A:** - This option is incorrect because, although some lymphomas may express CD3, MALT lymphoma specifically expresses B cell markers, not T cell markers like CD3.
- **Option B:** - This option is incorrect because, while some lymphomas may have specific markers, the key marker for MALT lymphoma is not listed here; CD20 is the hallmark.
- **Option C:** - This option might seem plausible but is incorrect because the specific and correct marker for MALT lymphoma is CD20.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that MALT lymphomas are often associated with chronic inflammation and infections, such as *Helicobacter pylori* infection in gastric MALT lymphoma. The presence of CD20 on MALT lymphoma cells makes these tumors responsive to rituximab, a therapeutic monoclonal antibody targeting CD20.

## **Correct Answer:** . CD20