CML is a blood cancer that begins in the bone marrow, where blood cells are made. It's linked to a specific genetic change known as the Philadelphia chromosome, which leads to the creation of an abnormal gene called BCR::ABL1. This gene produces a protein that causes uncontrolled cell growth. CML is unique because it shares features with other myeloproliferative neoplasms (MPNs), like stem cell origin and dysregulated proliferation.

CML typically progresses through phases, starting with the chronic phase, which is the least aggressive and most common. In this phase, patients may not show symptoms or may have mild symptoms like fatigue or weight loss. If untreated, CML can progress to more severe phases, known as the accelerated and blast phases, characterized by more aggressive symptoms and increased difficulty in treatment.

Diagnosing CML involves looking at the patient's blood and bone marrow to check for the Philadelphia chromosome. Tests like complete blood count (CBC) and polymerase chain reaction (PCR) help confirm the diagnosis. These tests are crucial as they not only confirm CML but also help in monitoring the disease's progression and response to treatment.

Understanding CML is the first step towards effective management and treatment.