**Question:** Mantle cell lymphomas are positive for all of the following, except -

A. CD5
B. CD20
C. CD23
D. CD10

**Correct Answer:** CD10

**Core Concept:**
Mantle cell lymphoma (MCL) is a subtype of non-Hodgkin lymphoma characterized by the presence of the t(11;14)(q13;q32) chromosomal translocation, which leads to the overexpression of cyclin D1 protein. These lymphomas typically involve the lymphatic system and often affect older adults. MCL cells express a variety of cell surface markers, which can be used to identify and diagnose the disease.

**Why the Correct Answer is Right:**
CD5 is a marker for activated T cells and a subset of mature B cells, including MCL cells. CD20 is a marker for activated B cells, including MCL cells. CD23 is found on mature B cells and plasma cells, also expressed in MCL cells. However, CD10 is a marker for immature B cells and is not expressed in MCL cells. Thus, CD10 is the correct answer as it is not expressed in MCL cells, while the other options are expressed in MCL cells.

**Why Each Wrong Option is Incorrect:**
CD5 is a marker for activated B cells, including MCL cells. CD20 is a marker for activated B cells, including MCL cells. CD23 is found on mature B cells and plasma cells, also expressed in MCL cells.

**Clinical Pearl:**
Understanding the expression pattern of various lymphoma markers is crucial for accurate diagnosis of lymphomas, including mantle cell lymphomas. Knowledge of these markers helps in differentiating MCL from other lymphomas and solid tumors with similar clinical presentations.