## Core Concept
Chronic Lymphocytic Leukemia (CLL) and Mantle Cell Lymphoma (MCL) are both types of B-cell lymphoproliferative disorders. They share some similarities but have distinct clinical and pathological features. Accurate differentiation between them is crucial for appropriate management.

## Why the Correct Answer is Right
The correct answer involves the use of specific immunohistochemical markers to differentiate CLL from MCL. CLL cells typically express **CD5**, **CD23**, and **CD20** (weakly), while MCL cells express **CD5** and **CD20** (strongly) but are **CD23 negative**. This difference in immunophenotypic profile helps in distinguishing CLL from MCL.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because while CLL and MCL may share some clinical features, the specific differentiation usually relies on immunophenotyping rather than clinical presentation alone.
- **Option B:** This option is incorrect as it does not accurately represent the specific markers used to differentiate CLL from MCL.
- **Option D:** This option is incorrect because, although cytogenetic and molecular features such as **IGHV mutation status** and **TP53 mutations** can provide prognostic information, they are not the primary method for differentiating CLL from MCL.

## Clinical Pearl / High-Yield Fact
A key clinical pearl is that the **CD5 and CD23 status** is pivotal in differentiating CLL (typically **CD5+ CD23+**) from MCL (typically **CD5+ CD23-**). Additionally, MCL often shows a **t(11;14) translocation** leading to overexpression of cyclin D1, which can be detected by immunohistochemistry or FISH, further aiding in the diagnosis.

**Correct Answer:** .