ECC 2015: Living Conditions and Gender Appear to Affect Incidence of Hodgkin Lymphoma
Living in overcrowded conditions appears to protect children and young adults against developing a particular type of Hodgkin lymphoma. This protective effect seems to suggest that infections earlier in life may stimulate the immune system to deal with future infections and cancerous cells more efficiently, said the researchers who made the discovery. They presented their results (Abstract 1414) at the 2015 European Cancer Congress in Vienna, Austria.
Richard McNally, BSc, MSc, DIC, PhD, a Reader in Epidemiology at the Institute of Health and Society at Newcastle University, said the causes of Hodgkin lymphoma are not well understood at present. To try to achieve better knowledge of this issue, the researchers decided to analyze all the 621 cases of Hodgkin lymphoma in patients aged 0–24 years recorded in the Northern Region Young Persons’ Malignant Disease Registry.
“Childhood lymphomas are more common in males, but analysis by sex has not been done very frequently. Additionally, the male-to-female ratio changes in Hodgkin lymphoma according to age, so we decided to take age into account, as well as other factors such as socioeconomic deprivation,” Dr. McNally said.
Hodgkin lymphoma occurrence peaks during young adulthood and again after age 55. The overall 5-year survival rate is around 85%. For the 0–24 year-old age group included in the study, it is about 93%.
Subtypes and Their Rate of Incidence
The researchers found five different subtypes of Hodgkin lymphoma among the patients studied: 247 cases of the nodular sclerosis type, in which the tumor nodules are large; 105 of mixed cellularity, where a mixture of different types of inflammatory cells are involved; 58 lymphocyte rich, the subtype with the best outcome; 68 “others”; and 143 “not otherwise specified.”
Overall, more males than females studied had Hodgkin lymphoma, but the male-to-female ratio varied by both age group and disease subtype. For the nodular sclerosis subtype, there were 130 males and 117 females, but this was reversed at ages 20–24, with 72 females and 55 males.
Deprivation was calculated using the four components of the Townsend Deprivation Index: household overcrowding, nonhome ownership, unemployment, and households with no car. The researchers found a decreased incidence of the nodular sclerosis subtype of Hodgkin lymphoma among those patients living in areas with more overcrowded households, and a 5% increase in the level of household overcrowding had the effect of halving the number of cases of this subtype.
However, for the “not otherwise specified” group, the reverse was seen, with overcrowding being associated with an increased incidence of this type of Hodgkin lymphoma, whereas deprivation seemed to have no effect on the incidence of the mixed cellularity and lymphocyte-rich subtypes.
“Our findings related to the nodular sclerosis subtype may suggest that the recurrent infections to which children living in overcrowded conditions are likely to have been exposed stimulate their immune systems and hence protect them against developing this type of cancer later in their childhood and early adult life. Those who have a genetic susceptibility to Hodgkin lymphoma and have been less exposed to infection through not living in such overcrowded conditions may have less developed immune systems as a result and are, therefore, at greater risk of developing this subtype,” said Dr. McNally.
Effect of Gender
“Another interesting finding is the preponderance of females with the nodular sclerosis subtype in the 20–24 age group. That this change takes place after puberty seems to suggest that estrogen may be responsible in some way. There are a lot of genes directly regulated by sex hormones, and they are obvious suspects. Alternatively, epigenetic changes influencing key genes, induced by sex hormones, may be responsible.”
“We knew already that recurrent infections may protect against childhood leukemia, and now it looks as we can add Hodgkin lymphoma, and, particularly its nodular sclerosis subtype, to the list. In order to further investigate the factors involved, prospective studies should investigate the hormonal changes and recurrent infections and their direct link to the risk of lymphoma, but such studies are difficult to do in rare diseases. A practical follow-up would be case control studies examining biological markers related to exposure to a multitude of infectious agents, and indeed to hormonal status itself, while genetic studies are another possibility,” Dr. McNally concluded.
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