Socio-economic risk patterns in Hodgkin lymphoma: not more, but new studies are warranted

For several decades, epidemiologists have worked with the understanding that the socio-economic environment in early life strongly influences the risk of Hodgkin lymphoma (HL), not only in childhood but also among adolescents and younger adults. [1,2] A wealth of evidence has supported this assumption, spanning from variation in age-specific incidence patterns between populations with different levels of socio-economic development or within populations at different time periods. Thus, a number of studies have linked the risk of HL in adolescence and in younger adults with a variety of correlates of childhood socioeconomical affluence, such as sibship size and structure, and housing. [3] While there can be little doubt that the first years of life play a pivotal role in HL epidemiology, the precise biological mechanisms underpinning this association have mostly remained elusive. Thus, almost automatically studies have continued to examine risk factors that have already comprehensively been explored before in HL research. In 2015, the shortcomings in our understanding of the etiology of HL resulting from this practice were highlighted in this journal by Glaser et al.[4] In a study of ethnic enclaves in California, these authors demonstrated that HL incidence varied substantially by the degree of ethnic acculturation, beyond what could be explained by the traditional measures of socio-economic status. [4] The current issue of the Leuekmia and Lymphoma features a new cohort study which illustrates how challenging the identification of the causes of HL continues to be. [5] Here, in an impressive prospective study, Levine et al. [5] followed a cohort of 2.3 million Israeli military conscripts who at pre-recruitment assessments had been examined clinically and provided information on socio-demographic characteristics including also personal, paternal and grandpaternal origins. The occurrence of HL in Israel is among the highest in the world,[6] and – as might have been expected – the study showed that HL incidence was lower among immigrant than Israeli-born conscripts. Consistent with the typical age-specific distribution of histological subtypes of classical HL, sub-analyses indicated that the difference in overall incidence according to immigration status was primarily explained by corresponding associations for nodular sclerosis classical HL. In contrast, no evidence of association with immigration status was seen for mixed cellularity classical HL. Noteworthy, the analyses also showed that among conscripts born in Israel incidence of HL did not vary by country of paternal/grandpaternal origin. [5] This is indeed unlike, e.g., among Asian Americans, in whom HL incidence in adolescents and younger adults seems consistently lower than in White Americans. [7] Other findings in the Israeli study reported here included associations between HL risk and body mass index and stature at presentation before military recruitment (both of which may have socio-economical connotations) and with female sex, and birth year. [5] Overall, the observations by Levine et al. confirm that exposures of significance to the risk of HL in early adulthood have already occurred before late adolescence, and also show that the transition to an Israeli childhood socio-economic environment is associated with a marked increase in the risk of HL, possibly even within the span of a single generation. None of these reported observations can be said to contribute