of Hodgkin Lymphoma
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.
Hodgkin lymphoma is an uncommon lymphoma, with 7,500 annual cases in the United States. Hodgkin lymphoma accounts for only 0.7% of all malignancies. At this time, the cause of Hodgkin lymphoma is unknown and researchers are trying to solve this problem. Scientists know that Hodgkin lymphoma is not caused by injury and it is not infectious. Scientists know that Hodgkin lymphoma occurs most commonly in people between the ages of 15 and 35 and in individuals over the age of 55. However, they cannot explain why one person gets Hodgkin lymphoma and another does not. By learning what causes this lymphoma, researchers hope to better understand how to prevent and treat it.
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.
Heredity and Genetic Factors
Siblings of patients with Hodgkin lymphoma have a higher than average chance of developing this lymphoma; however, because this lymphoma is so rare, this increased risk is minimal. Identical twins of patients with Hodgkin lymphoma are at no greater risk of developing Hodgkin lymphoma than other siblings. This strongly suggests that environmental factors are much more important than genetic factors in the development of Hodgkin lymphoma. It is a scientific mystery as to why only one of a pair of identical twins will develop Hodgkin lymphoma, since the genetics are identical and environmental exposures are similar, if not the same.
Rarely, Hodgkin lymphoma may occur in more than one family member, but it is not clear if this is due to genetic factors, environmental factors, or both. Populations of East Asian ethnic origin have a low incidence of Hodgkin lymphoma, while South Asian ethnic populations have a high incidence, which suggests a genetic predisposition. Any form of genetic or familial immunodeficiency may be associated with an increased incidence of Hodgkin lymphoma.
Environmental or Non-Genetic Factors
The fact that only one of a pair of identical twins usually develops Hodgkin lymphoma suggests that finding the specific cause for Hodgkin lymphoma will be difficult if not impossible. However, by studying large numbers of people all over the world, researchers have found certain factors that increase a person’s risk of getting Hodgkin lymphoma.
Many, but not all, studies show a consistent link between woodworking and Hodgkin lymphoma. Trichloroethylene is an organic chemical used in dry cleaning, metal degreasing and as a solvent for oils and resins and has been identified to cause liver and kidney cancer in animals. Exposure to trichloroethylene has been associated with an increased chance of developing Hodgkin lymphoma and other cancers. Machinists in the metal working industry have also been reported to have a higher than average incidence of Hodgkin lymphoma. Exposure to pesticides has been associated with an increased incidence of Hodgkin lymphoma in some, but not all, clinical studies.
Exposure to low levels of radiation may cause an increased incidence of Hodgkin lymphoma. Workers at some nuclear facilities have been found to have an increased incidence of pancreatic cancer and Hodgkin lymphoma compared to the normal population. An increased incidence of Hodgkin lymphoma has been reported in farmers compared to people living in cities.
Immunosuppressive or Cytotoxic Treatment of Other Lymphomas: Autoimmune lymphomas and cancers treated with immunosuppressive and/or cytotoxic chemotherapy drugs appear to increase the incidence of Hodgkin lymphoma. For instance, Hodgkin lymphoma has been reported after methotrexate treatment of rheumatoid arthritis.
Other Lymphomas and Hodgkin lymphoma: There is an increased incidence of Hodgkin lymphoma among people who are immunodeficient, regardless of whether this immunodeficiency is naturally occurring or medically induced. Therefore, researchers have difficulty determining whether associations are natural or due to treatment.
Some, but not all, clinical studies have reported an increased incidence of Hodgkin in individuals with the human immuno-deficiency virus (HIV). In one study from Africa, where HIV is very common, there was no association between HIV infection and Hodgkin lymphoma.
Viruses and Hodgkin lymphoma: The Epstein-Barr virus, which causes infectious mononucleosis, infects B lymphocytes and is found in cancer cells from some lymphoid malignancies including Burkitt’s lymphoma, nasopharyngeal carcinoma and Hodgkin lymphoma. Thus, people with a history of infectious mononucleosis appear to have an increased chance of developing Hodgkin lymphoma later in life. Researchers currently believe that early childhood exposure to the Epstein-Barr virus is not associated with an increased incidence of Hodgkin lymphoma, but late exposure, as with infectious mononucleosis, is associated with an increased chance of developing Hodgkin lymphoma.
The Epstein-Barr virus can be found in the biopsy samples of individuals with Hodgkin lymphoma. In one clinical study from Africa, 87% of patients with Hodgkin lymphoma tested positive for the Epstein-Barr virus. The relationship between the Epstein-Barr virus and Hodgkin lymphoma is complex and does not appear to be a direct cause and effect relationship. In other words, the Epstein-Barr virus can be found in individuals with Hodgkin lymphoma, but the reverse is not often true. While 90-95% of adults have evidence of an infection from the Epstein-Barr virus, only a small percentage of these individuals will ever develop Hodgkin lymphoma. It is thought that the development of Hodgkin lymphoma may be accompanied or triggered by viral reactivation. Scientists are still trying to understand why the peak incidence of Hodgkin lymphoma occurs in young individuals and have further speculated that the additional involvement of an as yet undetected second virus may be involved.
Cancer is largely a preventable illness. Two-thirds of cancer deaths in the U.S. can be linked to tobacco use, poor diet, obesity, and lack of exercise. All of these factors can be modified. Nevertheless, an awareness of the opportunity to prevent cancer through changes in lifestyle is still under-appreciated. The overwhelming majority of cases of Hodgkin lymphoma cannot be prevented since we do not know the cause.
Scientists around the world have been working on vaccine strategies against Epstein-Barr virus associated lymphomas. This work has been hampered by an inability to identify the characteristics of the virus when it remains dormant in the body. However, there is currently some optimism that vaccine trials aimed at controlling infectious mononucleosis, post-transplant lymphoproliferative lymphoma, nasopharyngeal carcinoma and Hodgkin lymphoma may soon be justified.
Diet: A poor diet is a fertile area for immediate individual and societal intervention to decrease the risk of developing certain cancers. Numerous studies have provided a wealth of information about the detrimental and protective factors of different foods.
There is convincing evidence that excess body fat substantially increases the risk for many types of cancer. While much of the cancer-related nutrition information cautions against a high-fat diet, the real culprit is an excess of calories. Studies indicate that there is little, if any, relationship between body fat and fat composition of the diet. These studies show that excessive caloric intake from both fats and carbohydrates have the same result of excess body fat. The ideal way to avoid excess body fat is to limit caloric intake and/or balance caloric intake with ample exercise.
It is still important, however, to limit fat intake, as evidence still supports a relationship between cancer and polyunsaturated, saturated and animal fats. Specifically, studies show that high consumption of red meat and dairy products can increase the risk of certain cancers. One strategy for positive dietary change is to replace red meat with chicken, fish, nuts and legumes.
High fruit and vegetable consumption has been associated with a reduced risk for developing at least 10 different cancers. This may be a result of potentially protective factors such as carotenoids, folic acid, vitamin C, flavonoids, phytoestrogens and isothiocyanates.
There is strong evidence that moderate to high alcohol consumption also increases the risk of certain cancers. One reason for this relationship may be that alcohol interferes with the availability of folic acid. Alcohol in combination with tobacco creates an even greater risk.
Exercise: Higher levels of physical activity may reduce the incidence of some cancers. According to researchers at Harvard, if the entire population increased their level of physical activity by 30 minutes of brisk walking per day (or the equivalent energy expenditure in other activities), we would observe a 15% reduction in the incidence of colon cancer.
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.
Hodgkin lymphoma is usually diagnosed because patients have signs and symptoms including a painless swelling in the lymph nodes in the neck, under the arm or in the groin; unexplained fevers; night sweats; unexplained weight loss and/or itchy skin.
In order for screening to be effective, patients at risk for Hodgkin lymphoma need to be identifiable. This is not currently possible, with the exception of identifying patients who have one of a few genetic lymphomas and screening them accordingly.
American Cancer Society. Cancer Facts & Figures 2017.