I'm currently undergoing tests for both bone marrow cancer and leukemia.  In my researching for "causes" I find that it's both a genetic DNA problem (not stated so below, but it is at other sites) and a radiation and chemically induced disease.  Those with backgrounds in agriculture, or chemical/biological work are at higher risk for this disease.  In searching my head for a background in any of this I remember while working in agriculture that I ran a small machine that applied some kind of copper compound to wheat prior to planting to make it resistant to disease.  I was supposed to be wearing a respirator while doing this because there was significant dust from the copper (a poison) but due to the heat and sweat I never wore it.  While in Asia I was sprayed from the air with DDT where they were trying to control malaria mosquitoes and could feel the spray hit my clothing, taste it in my mouth and yes inhaled it too.  This happened several times and was also along with everyone else sprayed with DDT on my body as we were deloused before returning to the USA.  Added to that I lived in the neighborhood of a copper smelter (within two miles) for several years where when the winds were right we could all taste the arsenic in the air.  A little closer to the smelter itself people couldn't keep their grass green because the arsenic also killed vegetation.  So, radiation and chemicals can and do come from many different sources.

http://en.wikipedia.org/wiki/Acute_lymphoblastic_leukemia

Pathophysiology

In general, cancer is caused by damage to DNA that leads to uncontrolled cellular growth and spread throughout the body, either by increasing chemical signals that cause growth, or interrupting chemical signals that control growth. Damage can be caused through the formation of fusion genes, as well as the dysregulation of a proto-oncogene via juxtaposition of it to the promoter of another gene, e.g. the T-cell receptor gene. This damage may be caused by environmental factors such as chemicals, drugs or radiation.

ALL is associated with exposure to radiation and chemicals in animals and humans. The association of radiation and leukemia in humans has been clearly established in studies of victims of the Chernobyl nuclear reactor and atom bombs in Hiroshima and Nagasaki. In animals, exposure to benzene and other chemicals can cause leukemia. Epidemiological studies have associated leukemia with workplace exposure to chemicals, but these studies are not as conclusive. Some evidence suggests that secondary leukemia can develop in individuals who are treated for other cancers with radiation and chemotherapy as a result of that treatment

I do not believe that anyone is genetically predestined to have leukemia or just about any other cancer, though certainly people can be genetically disposed to be more susceptible to getting leukemia and other cancers.  Much of the time genetics is blamed for cancers running in families when what actually is the case is that families tend to have the same lifestyles, diet, exposure to toxins, etc.

Radiation destroys bone marrow and that very well could lead to a much greater susceptiblity to leukemia. Bone marrow is at the heart of the natural immune system which is our natural first line of defense against cancer and other illness and is crucial to keeping cancer at bay if it has been acquired and beaten,

Interestingly, oleander extract has had very good success against leukemia.  Of course I mean extract from the commercial supplements, the patent medicine version or else the version made at home by carefully following exact tried and true directions.  Raw oleander is quite toxic and no one should try to make their own or handle it without knowing what they are doing.  Properly prepared it is essentially non-toxic when administered in proper amounts.