Information about the prevention of cancer and the science of screening appropriate individuals at high-risk of developing cancer is gaining interest. Physicians and individuals alike recognize that the best “treatment” of cancer is preventing its occurrence in the first place or detecting it early when it may be most treatable.
The chance of an individual developing cancer depends on both genetic and non-genetic factors. A genetic factor is an inherited, unchangeable trait, while a non-genetic factor is a variable in a person’s environment, which can often be changed. Non-genetic factors may include diet, exercise, or exposure to other substances present in our surroundings. These non-genetic factors are often referred to as environmental factors. Some non-genetic factors play a role in facilitating the process of healthy cells turning cancerous (i.e. the correlation between smoking and lung cancer) while other cancers have no known environmental correlation but are known to have a genetic predisposition, meaning a person may be at higher risk for a certain cancer if a family member has that type of cancer.
At this time, we do not know what causes CLL. Researchers are trying to solve this problem. CLL is predominantly a disease of older individuals, with a median age at diagnosis of 72 years, and it tends to be more common in men than in women.1 Nevertheless, it is still not possible to predict who will develop CLL and who will not. By learning what causes CLL, researchers hope to better understand how to prevent and treat it.
Heredity and Genetic Factors
Risk of CLL is higher among individuals with a family history of CLL,2 and is also higher in certain populations than others. Rates in the United States, for example, tend to be several times higher then rates in Asian countries.3 And within the United States, CLL rates are highest among whites (4.1 cases per 100,000 people per year), followed by African Americans (3.0 cases per 100,000 people per year), Hispanics (1.9 cases per 100,000 people per year), Native Americans (1.5 cases per 100,000 people per year), and Asian Americans (0.8 cases per 100,000 people per year).4
Whether these differences across populations reflect hereditary factors, environmental factors, or a combination of the two remains uncertain. However, familial aggregation of CLL suggests that inherited genetic factors may be important in this disease.
Environmental or Non-Genetic Factors
The role of environmental factors in CLL remains poorly understood. Although diet, exercise, and body weight appear to influence the risk of several types of cancer, there is little information about whether these factors influence risk of CLL.5 Some studies have suggested that CLL risk is increased in certain occupational groups, such as farmers or rubber industry workers, but these data are not conclusive.6
Because we do not know the cause of most cases of CLL, there is currently no established way to prevent the disease.
Screening and Early Diagnosis
For many types of cancer, progress in the areas of cancer screening and treatment has offered promise for earlier detection and higher cure rates. The term screening refers to the regular use of certain examinations or tests in persons who do not have any symptoms of a cancer but are at high risk for that cancer. When individuals are at high risk for a type of cancer, this means that they have certain characteristics or exposures, called risk factors that make them more likely to develop that type of cancer than those who do not have these risk factors. The risk factors are different for different types of cancer. An awareness of these risk factors is important because 1) some risk factors can be changed (such as smoking or dietary intake), thus decreasing the risk for developing the associated cancer; and 2) persons who are at high risk for developing a cancer can often undergo regular screening measures that are recommended for that cancer type. Researchers continue to study which characteristics or exposures are associated with an increased risk for various cancers, allowing for the use of more effective prevention, early detection, and treatment strategies.
Historically, CLL has been diagnosed at an advanced stage that typically involves the lymph nodes and bone marrow. More recently, however, the disease has frequently been detected in routine blood tests, allowing for earlier diagnosis. It is still not possible, however, to identify a high-risk group that would benefit from screening for CLL. Nor has it been demonstrated that early diagnosis of CLL improves survival.
1 Ries LAG, Melbert D, Krapcho M, Mariotto A, Miller BA, Feuer EJ, Clegg L, Horner MJ, Howlader N, Eisner MP, Reichman M, Edwards BK (eds). SEER Cancer Statistics Review, 1975-2004, National Cancer Institute. Bethesda, MD, http://seer.cancer.gov/csr/1975_2004/, based on November 2006 SEER data submission, posted to the SEER web site, 2007.
2 Caporaso N, Goldin L, Plass C et al. Chronic lymphocytic leukemia genetics overview. British Journal of Haematology. 2007;139:630-634.
3 Linet MS, Chartwright RA. The Leukemias. In: Schottenfeld D, Fraumeni JF Jr. eds. Cancer Epidemiology and Prevention (2nd ed). New York: Oxford University Press; 1996:841-892.
4 Surveillance, Epidemiology, and End Results (SEER) Program (www.seer.cancer.gov) SEER*Stat Database: Incidence – SEER 17 Regs Limited-Use, Nov 2006 Sub (2000-2004), National Cancer Institute, DCCPS, Surveillance Research Program, Cancer Statistics Branch, released April 2007, based on the November 2006 submission.
5 Linet MS, Schubauer-Berigan MK, Weisenburger DD et al. Chronic lymphocytic leukemia: an overview of aetiology in light of recent developments in classification and pathogenesis. British Journal of Haematology. 2007;139:672-686.
6 Blair A, Purdue MP, Weisenburger DD, Baris D. Chemical exposure and risk of chronic lymphocytic leukemia. British Journal of Haematology. 2007;139:753-761.