A 68 year old woman was admitted with a history of weakness for two months. On examination, cervical lymph nodes were found enlarged and spleen was palpable 2 cm below the costal margin. Her hemoglobin was 10.5 g/dl, platelet count 27 x 109/L and total leukocyte count 40 x 109/L, which included 80 % mature lymphoid cells with coarse clumped chromatin. Bone marrow revealed a nodular lymphoid infiltrate. The peripheral blood lymphoid cells were positive for CD19, CD5, CD20 and CD23 and were negative for CD79B and FMC-7. The histopathological examination of the lymph node in this patient will most likely exhibit effacement of lymph node architecture by?

**Core Concept**
The patient's presentation is suggestive of a chronic lymphocytic leukemia (CLL), characterized by the accumulation of mature lymphocytes in the peripheral blood, bone marrow, and lymphoid organs. CLL is a type of non-Hodgkin lymphoma (NHL) that is often associated with a nodular lymphoid infiltrate in the bone marrow.

**Why the Correct Answer is Right**
The patient's lymphoid cells are positive for CD19, CD5, CD20, and CD23, which are characteristic markers of CLL. The absence of CD79B and FMC-7 expression further supports this diagnosis. CLL cells often exhibit a specific immunophenotype, which can be used to distinguish them from other types of lymphoid neoplasms. The nodular lymphoid infiltrate in the bone marrow is a common feature of CLL, which can lead to effacement of the lymph node architecture.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because CLL is not typically associated with a diffuse large cell lymphoma (DLCL) pattern. DLCL is a different subtype of NHL that is characterized by a more aggressive clinical course and a distinct immunophenotype.

**Option B:** This option is incorrect because mantle cell lymphoma (MCL) is a different subtype of NHL that is characterized by a specific immunophenotype (positive for CD5, CD20, and CD23, but negative for CD19 and FMC-7). MCL often presents with a nodular lymphoid infiltrate in the bone marrow, but it is not the most likely diagnosis in this case.

**Option C:** This option is incorrect because follicular lymphoma (FL) is a different subtype of NHL that is characterized by a specific immunophenotype (positive for CD20 and CD10, but negative for CD5 and CD23). FL often presents with a nodular lymphoid infiltrate in the bone marrow, but it is not the most likely diagnosis in this case.

**Option D:** This option is incorrect because small lymphocytic lymphoma (SLL) is a different subtype of NHL that is characterized by a similar immunophenotype to CLL (positive for CD19, CD5, CD20, and CD23). However, SLL often presents with a more pronounced lymphadenopathy and a less pronounced leukocytosis compared to CLL.

**Clinical Pearl / High-Yield Fact**
CLL is often associated with a nodular lymphoid infiltrate in the bone marrow, which can lead to effacement of the lymph node architecture. CLL cells often exhibit a specific immunophenotype, which can be used to distinguish them from other types of lymphoid neoplasms.

**Correct Answer:** C.

✓ Correct Answer: A. A monomorphic lymphoid proliferation with admixed proliferation centers