The short answer to your question is that it can be classified as a genetic disease because it is caused by a mutation betwen chromosomes 9 and 22. I shall give a short explanation. Chronic myelogenous leukemia (CML; also known as chronic myeloid leukemia or chronic granulocytic leukemia) is a cancer of the blood system in which too many white blood cells (WBCs) are made in the bone marrow. In the early stages of CML (the chronic phase), these excess WBCs mature normally. In contrast, excess WBCs in late CML (the accelerated and acute phases) do not mature. the average age of people with CML is around 66 years, CML mostly affects adults, although 2 percent of CML patients are children. In almost everyone with CML, the genetic material (chromosomes) in the leukemia cells has an abnormal feature called the Philadelphia chromosome. Without going into a lengthy technical discussion, I shall just mention that the Philadelphia chromosome is an acquired mutation ? that is, a person is not born with it and it is not passed on to their children. Exactly why the Philadelphia chromosome forms is unknown in most cases, although exposure to ionizing radiations (such as during the atomic bomb explosions in Japan) has been shown to cause CML. CML is divided into three phases depending on the maturity of the leukemia WBCs. In the Chronic phase, there are mostly mature leukemia WBCs in the blood and bone marrow and there may be no symptoms of leukemia. This phase lasts from several months to several years, with an average duration of five years. The Accelerated phase shows some immature leukemia WBCs in the blood and bone marrow (between 5 percent and 30 percent). Patients may have fever, poor appetite and weight loss. The leukemia cells may have new chromosome changes, in addition to the Philadelphia chromosome. The Acute phase is also called the blast phase or blast crisis. In this phase, there are mostly immature WBCs in the blood and bone marrow (more than 30 percent). Symptoms such as anemia and recurring infections are typical.
Patients may have fever, poor appetite and weight loss. The leukemia cells may have new chromosome changes, in addition to the Philadelphia chromosome.
I add some links with information that you may find of interest http://www.cmlsupport.com/ http://www.leukemia-lymphoma.org/
Hope this helps