This study compares changes in P16INK4A expression and plasma proteomic signatures of specific organ age pre- and post-chemotherapy in women treated with adjuvant chemotherapy for early-stage breast cancer. It aims to determine if biological and accelerated immune aging, assessed using T cells from peripheral blood, represents aging in different organs. Patients receiving chemotherapy, especially adjuvant regimens that include anthracyclines and taxanes, often experience late development of cardiac toxicity, functional loss, and cognitive decline. Comparing baseline characteristics with organ aging before therapy might identify patients at the highest risk for chemotherapy complications. For example, this is clinically significant for patients whose therapy includes taxanes or other drugs known to cause peripheral neuropathy. Identifying aging in the neurological or vascular systems before treatment might lead to changes in regimens. Determining accelerated aging in specific organs allows for investigating interventions to mitigate organ damage. For instance, identifying patients at the highest risk of cardiac aging after treatment could lead to testing the effects of exercise, senolytics, and other strategies to reduce the risk of long-term heart disease.