"Frailty" is a term used to refer to a state characterised by enhanced vulnerability to, and impaired recovery from, stressors, when compared to a non-frail state, which is increasingly viewed as a loss of resilience. With increasing life expectancy and the associated rise in years spent with physical frailty, there is a need to understand the clinical and physiological features of frailty and the factors driving it. We describe the clinical definitions of age-related frailty and their limitations in allowing us to understand the pathogenesis of this prevalent condition. Given age-related frailty manifests in the form of functional declines such as poor balance, falls and immobility, as an alternative we view frailty from a physiological viewpoint and describe what is known of the organ-based components of frailty, including adiposity, the brain, and neuromuscular, skeletal muscle, immune and cardiovascular systems, as individual systems and as components in multisystem dysregulation. By doing so we aim to highlight current understanding of the physiological phenotype of frailty and reveal key knowledge gaps and potential mechanistic drivers of the trajectory to frailty. We also review the studies in humans that have intervened with exercise to reduce frailty. We conclude that more longitudinal and interventional clinical studies are required in older adults. Such observational studies should interrogate the progression from a non-frail to a frail state, assessing individual elements of frailty to produce a deep physiological phenotype of the syndrome. The findings will identify mechanistic drivers of frailty and allow targetted interventions to diminish frailty progression.

BACKGROUNDAdrenocortical carcinoma (ACC) is rare, nearly always fatal, and to the authors' knowledge has few nonsurgical treatment options. Based on in vitro studies demonstrating the efficacy of mitotane as a P‐glycoprotein (Pgp) antagonist, and expression of high levels of Pgp in ACC, the authors conducted a study of infusional doxorubicin, vincristine, and etoposide with oral mitotane ± surgical resection in patients with metastatic ACC.METHODSThirty‐six patients with metastatic ACC received daily oral mitotane (mean, 4.6 g/day) and 96‐hour infusional doxorubicin (10 mg/m2/day), etoposide (75 mg/m2/day), and vincristine (0.4 mg/m2/day). Four responding patients (11%) underwent surgery.RESULTSThirty‐five patients were evaluable; all had metastatic disease. Eleven patients had not undergone resection of the primary tumor. Approximately 53% of patients had functional tumors. A total of 190 cycles were administered to 36 patients. Responses were observed in 8 patients (22%): 1 complete, 4 partial, and 3 minor responses. The mean duration of response was 12.4 months. Using a landmark method, the median survival of patients who did not respond to chemotherapy was 11.6 months from a point 4 months after the initiation of therapy, whereas that of 8 patients who demonstrated a response to chemotherapy was 34.3 months from that same landmark. High levels of Pgp expression were documented in nine of nine tumors. Mitotane levels > 10 μg/mL, previously shown to antagonize Pgp in vitro, were achieved in 25 of 36 patients (69%). However, rhodamine efflux from CD56‐positive cells was not impaired, suggesting poor in vivo Pgp inhibition. The predominant Grade 3/4 toxicity (according to the Common Toxicity Criteria of the National Cancer Institute) was neutropenia in 66% of cycles; however, fever occurred in only 3% of cycles. Daily mitotane was associated with Grade 1/2 nausea, diarrhea, fatigue, and neuropsychiatric changes in 31 of 36 patients (86%).CONCLUSIONSUsing a combination regimen of daily mitotane with infusional doxorubicin, vincristine, and etoposide in patients with metastatic ACC, responses were observed in 22% of patients. The superiority of this combination over single‐agent mitotane is uncertain. The side effects of mitotane made treatment difficult. More effective Pgp antagonists are needed. Cancer 2002;94:2333–43. © 2002 American Cancer Society.DOI 10.1002/cncr.10487