Incidence of and survival from childhood cancer : the role of social and family factors in childhood cancer

Abstract

Introduction: Social inequalities, both within countries and between countries, influence the occurrence of and survival from cancer, including childhood cancer. This dissertation aimed to gain further insight into social inequalities in childhood cancer on the national level within a country and also between countries with different levels of socioeconomic development. The first objective was to obtain a better understanding of the reported geographical differences in childhood cancer worldwide by studying incidence patterns in a Sub-Saharan African country (with a diverse racial/ethnic population) and comparing the findings to the incidence patterns of a representative high-income country (Germany). The second objective was to investigate survival from childhood cancers in relation to social and family factors within high-income countries. Methods: The two objectives were addressed by seven conceptually independent but topic-wise interrelated studies. Four studies provided the core manuscripts for this thesis: i) childhood cancer incidence patterns by race in South Africa, and in comparison to Germany; ii) survival from acute lymphoblastic leukaemia (ALL) in relation to socio-demographic background in Germany; iii) survival from ALL in relation to family factors in Germany; iv) survival from childhood haematological malignancies in relation to family factors in Denmark. Data from the South African National Cancer Registry, the German Childhood Cancer Registry, a former German case-control study, as well as from the Danish registries served as the basis for these studies. The incidence data were analysed by applying descriptive epidemiological methods. Kaplan-Meier curves and Cox proportional hazard models were used for the survival analyses. Results: Substantial differences in the reported incidence rates were observed within South African racial groups, with lowest rates among Black children and highest among White children. There were also considerable differences between White children in South Africa and in Germany, but the differences varied markedly by cancer type and by age at diagnosis. Social and family characteristics were found to be associated with survival from childhood cancers, although not consistently between Germany and Denmark and not across cancer types. An impact of socioeconomic factors on survival from ALL was not observed for either Germany or Denmark, however a beneficial effect of higher maternal education among children with non-CNS solid tumours in Denmark was observed. Higher birth order and having siblings was associated with poorer survival among childhood haematological cancer patients in Denmark, with associations being suggestive for ALL and non-Hodgkin lymphoma but stronger and statistically significant for acute myeloid leukaemia. Similarly, most associations with family factors were suggestive for survival from ALL in German children. Highest survival in Germany was seen for second-born children. Patterns of associations between parental age and survival from childhood cancers were diverse across studies. Discussion: Findings of this dissertation highlight social inequalities in childhood cancer with respect to reported incidence differences between racial groups in South Africa and compared to Germany. Furthermore, survival differences between social groups in Germany and Denmark were observed, although not consistently across cancer types. To reduce those observed social inequalities in childhood cancer, a thorough understanding of the underlying mechanisms and pathways is needed. Observed incidence differences in South Africa might be, at least to some extent, due to socio-cultural factors related to access and utilization of health care services rather than reflecting actual differences in cancer risks. Under-ascertainment of cases may not only drive the findings for South Africa but the global reported geographical patterns of childhood cancer incidence. Despite highly specialized and standardised treatment and free health services for all children in Germany and Denmark, not all children benefit equally from improvements in childhood cancer survival. Further studies are warranted to gain knowledge on the impact of social and family factors on childhood cancer survival in other populations and to identify underlying pathways.