A team of researchers led by Dr. Dr Richard McNally, a Reader in Epidemiology at the Institute of Health and Society, Newcastle University, recently found that living in overcrowded circumstances protects children and young people against developing a specific type of Hodgkin lymphoma (HL). The findings suggest that infections occurring early in life might incite the immune system to deal with foreign agents and cancerous cells more efficiently in future life.
Dr. McNally, who will present the study findings at the 2015 European Cancer Congress, said that at present time the causes of HL are still not well understood. To improve the understanding of the causes behind HL development, the research team examined the clinical records of 621 patients with HL aged 0-24 years. Data was retrieved from 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 HL according to age, so we decided to take age into account, as well as other factors such as socio-economic deprivation,” said Dr McNally in a recent news release.
During young adulthood the occurrence of HL peaks and again in individuals over 55 years of age. The overall five-year survival rate of HL is about 85%, and for the age group included in the research (0-24 year-old) is about 93%.
In the study, the team found five sub-types of HL in the cases analyzed, of which 247 were of nodular sclerosis (NS) type (involving large tumour nodules); 105 were of mixed inflammatory cellularity; 58 were lymphocyte rich (the HL sub-type with the best prognosis); 68 were considered as ‘others’; and 143 cases were ‘not otherwise specified’ (NOS).
The results revealed that compared to females, males had a higher incidence of HL, however, there was a variation in the male-female ratio by HL sub-type and age group. The results also showed that 117 females and 130 males were diagnosed with the NS subtype, however, at ages 20-24, this ratio was inverted to 72 females and 55 males.
The team calculated deprivation using the four factors of the Townsend deprivation score, which includes non-home ownership, household overcrowding and households with no car and unemployment. The results revealed there was a decrease in HL NS sub-type among those that lived in areas with overcrowded households. Furthermore, an increase of 5% in the level of household overcrowding further reduced this number.
When considering HL NOS subtype, the results showed the opposite: overcrowding was found to be associated with an increase in NOS incidence. On the other hand, deprivation did not have an effect on the incidence of lymphocyte-rich and mixed cellularity HL sub-types.
“Our findings related to the NS 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 HL and have been less exposed to infection through not living in such over-crowded conditions may have less developed immune systems as a result, and are, therefore, at greater risk of developing this sub-type,” said Dr McNally.
“Another interesting finding is the preponderance of females with the NS sub-type in the 20-24 age group. That this change takes place after puberty seems to suggest that oestrogens 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 – changes in the way genes are switched on and off – influencing key genes, induced by sex hormones, may be responsible. We knew already that recurrent infections may protect against childhood leukaemia, and now it looks as we can add Hodgkin lymphoma, and, particularly its NS 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,” he concluded.
Professor Peter Naredi, the ECCO scientific co-chair of the Congress, who was not involved in the research, commented: “These are interesting observations about a number of factors that may influence the possibility of developing Hodgkin lymphoma or, conversely, protect against it. Results of the case studies referred to by the presenter should add further to our knowledge of this subject.”