Association of cancer with functional decline at old age- a longitudinal study in Danish twins

Introduction: There is evidence that older adults with cancer have a higher risk of functional decline than cancer-free older adults. However, few studies are longitudinal, and none are twin studies. Thus, we aimed to investigate the relationship between cancer and functional decline in older adult (aged 70+ years) twins.
Materials and Methods: Cancer cases in Longitudinal Study of Aging Danish Twins were identified through the Danish cancer registry. Functional status was assessed using Hand Grip strength (HGS) (6 years follow-up), and self-reported questions on mobility (10 years follow-up) and cutoffs were defined to assess functional decline. Cox regression models were performed for all the individual twins. In addition, we extended the analysis to discordant twin pairs (twin pairs with one having cancer and the other being cancer-free), to control to a certain extend for (unmeasured) shared confounders (genetic and environmental factors).
Results: The analysis based on individual twins showed that individual twins with cancer are at increased hazard of worsening HGS (HR = 1.37, 95% CI: 1.04,1.80) than cancer-frees. Among the discordant twin pairs, twins with cancer had a higher hazard of worsening HGS (HR = 3.50, 95% CI: 1.15,10.63) than cancer-free cotwins. In contrast, there was no evidence of a difference between hazard of experiencing mobility decline for cancers compared to cancer-frees, in both individual twins and discordant twin pairs analyses.
Discussion: Cancer was associated with HGS functional decline in old individual twins and discordant pairs. Our results strengthen the importance of comprehensive geriatric assessment in older adults with cancer, as well as the importance of routine assessment of functional status. Promoting physical activity through exercise training programs could enable to prevent functional decline in older adults with cancer.