**Question:** True regarding multiple myeloma is all. except:

A. Multiple myeloma is a plasma cell disorder characterized by the clonal expansion of plasma cells in the bone marrow.
B. The primary site of multiple myeloma is the liver.
C. Multiple myeloma is a rare disease, affecting only 2-3% of all hematological malignancies.
D. The diagnosis of multiple myeloma is based on a negative bone marrow aspiration and biopsy.

**Correct Answer:**

**Core Concept:** Multiple myeloma is a plasma cell disorder characterized by the clonal expansion of plasma cells in the bone marrow. Plasma cells are a type of white blood cell that produce antibodies, and the abnormal expansion of these cells leads to the production of monoclonal immunoglobulins (mAbs or paraproteins) in the blood and urine.

**Why the Correct Answer is Right:**

Multiple myeloma affects the bone marrow, where plasma cells are produced. The clonal expansion of plasma cells leads to the production of monoclonal immunoglobulins, which can cause various symptoms and complications. Multiple myeloma is not a disease affecting the liver, making option B incorrect.

**Why Each Wrong Option is Incorrect:**

Option C is incorrect because multiple myeloma is a common hematological malignancy, accounting for approximately 10% of all hematological malignancies. Though rarer than lymphomas and leukemia, multiple myeloma is not as rare as stated in option C, which is a misconception.

Option D is incorrect because the definitive diagnosis of multiple myeloma requires evidence of bone marrow involvement, which is confirmed through bone marrow aspiration and biopsy. A negative result from these tests does not rule out multiple myeloma, making the statement false.

**Clinical Pearl:**

Multiple myeloma is a complex disease with diverse presentations and complications. It is essential for medical professionals to recognize and diagnose this disorder accurately, as appropriate treatment and prognosis depend on an accurate diagnosis. A thorough understanding of the clinical manifestations, pathophysiology, diagnostic criteria, and treatment options is vital for medical professionals dealing with hematological malignancies.