Cardiorespiratory Fitness is a Strong, Independent Predictor of Radiation Induced Fatigue in Breast Cancer

Abstract

Fatigue is among the most common but most poorly understood toxicities of patients undergoing radiation treatment for primary breast cancer, predisposing to poor quality of life, treatment non-compliance and comorbidity. In this prospective study, we sought to investigate whether an integrative measure of cardiopulmonary function under exercise conditions (cardiorespiratory fitness as evaluated by peak oxygen consumption, VO2peak) predicted fatigue in patients with early stage breast cancer undergoing radiation treatment. Patients with stage Tis-T2N0M0 breast cancer undergoing radiation to the breast performed a symptom-limited cardiopulmonary exercise test (CPET) on an electronic motorized treadmill test with 12-lead ECG monitoring (Mac® 5000, GE Healthcare) to assess cardiorespiratory fitness (VO2peak; ml O2.kg-1.min-1) according to standard procedures. Fatigue was assessed by the FACIT fatigue scale survey. Both assessments were performed during or after radiation therapy (typically within 30 days). To isolate the effects of radiation on fatigue and VO2peak, patients who received cytotoxic chemotherapy were excluded. All patients were treated with an opposed tangent technique to a dose of 4240 cGy in 16 fractions +/- a lumpectomy bed boost of 1000 cGy in 4 fractions. Twenty-eight patients (median age: 51.5, range 31-71) successfully performed both CPET and the FACIT surveys. The mean VO2 peak was 26.7 ml O2.kg-1.min-1(range 16.7- 41.7). The mean fatigue score was 38.6 (range 10-52, lower values indicating more fatigue). In age-adjusted analysis, lower VO2peak was a significant predictor of fatigue (r (25) = 0.49, n = 28, p = 0.009). Radiation-induced fatigue appears to be driven by a decrease in global cardiopulmonary function. Larger prospective studies are needed to further investigate this novel finding.