Biomarkers of aging (with a clinical potential in oncology)

Frailty is a result of underlying physiologic processes associated with aging that lead to poor functional reserve. With increasing degrees of frailty, the ability to recover from major stresses on the body such as cancer treatment becomes more difficult. Varying degrees of frailty can be subtle, which explains the difficulty of distinguishing which older adults will have excess toxicity from cancer therapy and ones will tolerate it well. Thus, a biomarker of aging would be a very useful tool to predict toxicity and functional decline with cancer treatment and guide treatment decisions for older patients. Based on the large body of work in the field of aging research, several processes have emerged as hallmarks of the aging process. There is a decline of the lymphocyte component of the total leukocyte count. Systemic inflammation increases and likely contributes to age-related diseases. Telomere length decreases with cellular replication over time. Finally, repeated exposure to environmental stress results in cellular senescence. Researchers are now exploring biomarkers of these processes and their potential application in geriatric oncology. While they may not be pure aging biomarkers, they may be characterized as biomarkers of frailty that have the potential to identify patients at increased risk for adverse events, functional decline, and poorer survival related to cancer treatment. This chapter will discuss the characteristics of an aging biomarker, the various markers that have been investigated, and the evidence for the use of these biomarkers in older adults with cancer.