CML Characteristics: Identifying the False Statement

Chronic Myeloid Leukaemia (CML) is a type of cancer affecting the blood and bone marrow. It originates from a specific genetic mutation. Let's examine each statement to find the one that is NOT true.

Option 1: Clonal Malignancy

This statement is true. CML originates from a single, mutated hematopoietic stem cell. This abnormal cell then proliferates, leading to a population of identical (clonal) cancerous cells.

Option 3: Defining BCR-ABL1 Fusion Gene

This statement is true. CML is characteristically defined by the presence of the Philadelphia chromosome, which results from a reciprocal translocation between chromosomes 9 and 22, denoted as $t(9;22)$. This translocation creates the $BCR-ABL1$ fusion gene, the primary driver of the leukaemia.

Option 4: Survival with TKI Therapy

This statement is generally considered true in the modern treatment era. Tyrosine Kinase Inhibitors (TKIs) have drastically improved outcomes for CML patients. Survival rates are high, with 10-year survival frequently reported to be around 85% or even higher with consistent TKI therapy.

Option 2: Risk in Monozygotic Twins

This statement is NOT true. While monozygotic (identical) twins share the same genetic makeup, CML is primarily caused by acquired somatic mutations (like the $BCR-ABL1$ fusion gene), not inherited predisposition. The risk for developing CML is not significantly increased simply by being a monozygotic twin. Concordance rates in identical twins are low, indicating that factors beyond genetics play a crucial role, and it's not an inherited condition that increases risk within twin pairs.