Chronic myelogenous leukemia is generally caused by a genetic mutation (BCR-ABL) that an individual acquires during his/her lifetime. This mutation isn’t transmissible, meaning that isn’t obtained from a parent and isn’t passed along to a child.
A number of environmental factors, such as long-term exposure to organic solvents (notably benzene), have been implicated in the development of CML. A more common toxin to which people expose themselves is cigarette smoke, but few studies have investigated the possible links with CML (and no studies have looked at second-hand smoke).
A study in Sweden found no association between CML and cigarette smoking (Bjork and colleagues. Occup Environ Med 2001;58:722-727). However, more recent studies have suggested that chronic, heavy smokers do have a greater risk of developing CML. The National Institutes of Health-American Association of Retired Persons conducted a Diet and Health Study in 1995-1996, and followed up the results a decade later (Kabat and colleagues. Cancer Epidemiol Biomarkers Prev 2013;22:848-854). During that 10-year span, about 3 in 10,000 people developed CML. Heavy smokers (more than 20 cigarettes per day) had a 50% higher risk of developing CML compared to never smokers. The other important lifestyle factor was obesity, which had a similar impact on CML risk. For people with a body-mass index (BMI) over 30 (e.g. a 183-cm [6-foot] man weighing 100 kg (220 lbs) or a 163-cm [5-foot 4 inch] woman weighing 80 kg [175 lbs]), there was a 45% higher risk of CML.
Perhaps what is more important is the impact of continuing to smoke after the diagnosis. An early study before the TKI era found that smoking substantially increased the risk of progressing from chronic-phase to blast-crisis CML (Herr and colleagues. Am J Hematol 1990;34:1-4). On average, smokers progressed to blast-crisis CML and died within 30 months, about a year sooner than non-smokers. So smoking appears to adversely affect the underlying disease process.
It isn’t known if smoking has the same impact on survival in people on a TKI, but it’s fair to say that smoking is unlikely to have a benefit. One area that has been studied is smoking and bone marrow transplantation (Marks and colleagues. Biol Blood Marrow Transplant 2009;15:1277-1287). An analysis of the Center for International Bone and Marrow Transplant Research database found that smokers had much higher rates of relapse and death. At five years, the relapse risk was 67% higher in smokers compared to non-smokers. At five years, the treatment-related mortality risk was almost double in smokers compared to non-smokers (50% vs. 28%).
It’s important to note that the problems caused by smoking appear to be reversible – so it’s never too late to quit. A U.S. study recently reported that the risk of developing CML steadily declined in people who quit smoking (Musselman and colleagues. Cancer Epidemiol 2013;37:410-416). It was a slow process, but people who had kicked the habit for 30 years or more had the same risk of developing CML as people who had never smoked.