Aims
To evaluate for differences in demographic, clinical and genetic characteristics (cytokine gene polymorphisms) and subgroups of patients undergoing radiotherapy and their family caregivers (FCs) who differ in their reported physical, psychological, social and spiritual well-being.

Methods
Secondary data from 167 oncology patients undergoing radiotherapy and 85 of their FCs were analysed. Growth mixture modelling identified latent classes of individuals based on Quality of Life (QOL) - Patient/Cancer Survivor subscale scores obtained prior to, during, and for four months following radiotherapy (taking the patient-FC dyad into account). Demographic, clinical and genetic characteristics (single nucleotide polymorphisms (SNPs) and their haplotypes among 15 cytokine candidate genes) were investigated for differences between the classes identified using chi-square, t-tests and logistic regression.

Results
Two latent QOL groups were found across the physical, psychological and social well-being subscales. Across these domains, the largest percentage of participants had better well-being (58.5% to 64.0%) and a smaller percentage had worse well-being (36.0% to 41.5%). Age, comorbidities, gender, Karnofsky Performance Status, and having children at home were associated with QOL (p<.05), often across multiple dimensions. Between group differences in social well-being was also associated with SNP variation in nuclear factor kappa beta 2 (NFKB2). Carrying one or two doses of the rare allele was associated with decreased odds of belonging to the lower social well-being class (OR (95% CI) = .46 (.21, .99), p=.049).

Conclusions
Patients and FCs at greatest risk of worse QOL across multiple dimensions of QOL were those who are younger, female, belong to an ethnic minority group, have children at home, have multiple comorbid conditions or have a lower functional status. Understanding genetic determinants of QOL may contribute to the development of molecular tests that identify high risk patients prior to the initiation of treatment to enable preventative intervention to improve patient outcomes.