Which of the following is not compatible with a diagnosis of juvenile myelomonocytic leukemia?
**Core Concept**
Juvenile myelomonocytic leukemia (JMML) is a rare and aggressive type of leukemia that primarily affects children. It is characterized by the clonal proliferation of myelomonocytic cells, which are a type of white blood cell. The diagnosis of JMML is often made based on a combination of clinical features, laboratory findings, and molecular genetic analysis.
**Why the Correct Answer is Right**
The correct answer is related to the distinct clinical and laboratory features that differentiate JMML from other types of leukemia. In JMML, there is typically an increase in the number of monocytes and neutrophils in the peripheral blood, with a characteristic decrease in the number of platelets. The bone marrow is often hypercellular, with a predominance of myelomonocytic cells. Molecular genetic analysis often reveals mutations in the NRAS, NF1, or PTPN11 genes.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is a common feature of JMML. The disease is characterized by an increase in the number of monocytes and neutrophils in the peripheral blood.
**Option B:** This option is also incorrect because it is a common feature of JMML. The bone marrow is often hypercellular, with a predominance of myelomonocytic cells.
**Option C:** This option is incorrect because it is not a characteristic feature of JMML. Unlike acute lymphoblastic leukemia (ALL), JMML is not typically associated with a high percentage of lymphoblasts in the bone marrow.
**Clinical Pearl / High-Yield Fact**
A key feature of JMML is the presence of a characteristic "cohesive band" of monocytes in the peripheral blood smear. This finding is often used as a diagnostic criterion for the disease.
**Correct Answer:** D