Decomposition of the population attributable fraction for two exposures

Contribution of Polygenic Risk to Hypertension Among Long-Term Survivors of Childhood Cancer

Background

Childhood cancer survivors experience significantly higher rates of hypertension, which potentiates cardiovascular disease, but the contribution and relationship of genetic and treatment factors to hypertension risk are unknown.

Objectives

This study sought to determine the contribution of a blood pressure polygenic risk score (PRS) from the general population and its interplay with cancer therapies to hypertension in childhood cancer survivors.

Methods

Using 895 established blood pressure loci from the general population, we calculated a PRS for 3,572 childhood cancer survivors of European ancestry from the Childhood Cancer Survivor Study (CCSS) original cohort, 1,889 from the CCSS expansion cohort, and 2,534 from the St. Jude Lifetime Cohort. Hypertension was assessed using National Cancer Institute criteria based on self-report of a physician diagnosis in CCSS and based on blood pressure measurement in the St. Jude Lifetime Cohort.

Results

In the combined sample of 7,995 survivors, those in the top decile of the PRS had an odds ratio (OR) of 2.66 (95% confidence interval [CI]: 2.03 to 3.48) for hypertension compared with survivors in the bottom decile. The PRS-hypertension association was modified by being overweight/obese (per standard deviation interaction OR: 1.13; 95% CI: 1.01 to 1.27) and exposure to hypothalamic-pituitary axis radiation (per standard deviation interaction OR: 1.18; 95% CI: 1.05 to 1.33). Attributable fractions for hypertension to the PRS and cancer therapies were 21.0% and 15.7%, respectively; they jointly accounted for 40.2% of hypertension among survivors.

Conclusions

A blood pressure PRS from the general population is significantly associated with hypertension among childhood cancer survivors and contributes to approximately one quarter of hypertension risk among survivors. These findings highlight the importance of screening for hypertension in all childhood cancer survivors and identifying higher-risk subgroups.

Attributable fraction for multiple risk factors: Methods, interpretations, and examples

The attributable fraction is the candidate tool to quantify individual shares of each risk factor on the disease burden in a population, expressing the proportion of cases ascribable to the risk factors. The original formula ignored the presence of other factors (i.e. multiple risk factors and/or confounders), and several adjusting methods for potential confounders have been proposed. However, crude and adjusted attributable fractions do not sum up to their joint attributable fraction (i.e. the number of cases attributable to all risk factors together) and their sum may exceed one. A different approach consists of partitioning the joint attributable fraction into exposure-specific shares leading to sequential and average attributable fractions. We provide an example using Italian case-control data on oral cavity cancer comparing crude, adjusted, sequential, and average attributable fractions for smoking and alcohol and provide an overview of the available software routines for their estimation. For each method, we give interpretation and discuss shortcomings. Crude and adjusted attributable fractions added up over than one, whereas sequential and average methods added up to the joint attributable fraction = 0.8112 (average attributable fractions for smoking and alcohol were 0.4894 and 0.3218, respectively). The attributable fraction is a well-known epidemiological measure that translates risk factors prevalence and disease occurrence in useful figures for a public health perspective. This work endorses their proper use and interpretation.