[Abstract] Changing epidemiology and trends in incidence of childhood acute lymphoblastic leukaemia in Scotland: An analysis of the national cancer registration data, 1971-2020

Introduction: Acute lymphoblastic leukaemia (ALL) is the most common haematological malignancy in children (aged 0-14 years), accounting for about 25% of all childhood cancers. The highest incidence in observed in developed countries in Europe, North America and Oceania. The disease is relatively more common in males than females, with a M:F ratio of about 1.3-1.5:1. The aetiology of ALL is not well understood – this includes genetic (e.g. Down’s syndrome) and environmental (e.g. exposure to high levels of ionizing radiation) factors and the ‘delayed infection/population mixing hypotheses. We conducted a retrospective population-based cohort study to examine whether there have been changes in the epidemiology of ALL in Scotland during the past five decades.

Material and method: Individual-level, national (population-based) cancer registration data for patients diagnosed with childhood (age 0-14 years) ALL (ICD-10 code, C91.0) in Scotland from 1970-2020 were obtained from the Scottish Cancer Registry, Public Health Scotland. Average annual incidence rates were calculated by gender during the 10 five-year time periods (1971-75 to 2016-20). The percentage (%) change in the incidence rates in each gender was calculated as the change in the average annual incidence rate from the first (1971-75) to the last time period (2016-20). The average annual percentage change (i.e. year-on-year increase in incidence rates during 1971-2020) was estimated using the slope of the linear trend line fitted to the incidence rates by year of diagnosis.

Results and discussion: During the 50-year study period (1971-2020), a total of 2,951 new cases of childhood (age, 0-14 years) ALL were registered in Scotland (56.5% males, 43.5% females). The average annual incidence rates increased by about 56% in males (from 2.7/100,000 children in 1971-75 to 4.2/100,000 in 2016-20), and about 95% in females (from 2.1/100,000 in 1970-75 to 4.1/100,000 in 2016-20). The average annual percentage change in incidence rate was 1.2% in males and 1.6% in females.

Conclusions: It appears that there has been a small but steady increase in the incidence of childhood ALL in Scotland during the past 5 decades. Some of this increase may be due to the improvement in diagnostic procedures during this period. Although generally the disease is more common in males, our study showed that the incidence rates in recent years have become similar in both genders (4.2/100,000 vs. 4.1/100,000). There was also a much higher increase in the incidence rates in females than in males (95% vs. 56%) over the study period. This unexpected relatively greater increase in incidence in female children needs further investigation.