Key result
Untreated breast cancer in rats reduces exercise tolerance despite preserved VO2max and cardiac function.
Why the study?
The isolated effect of breast cancer on maximal oxygen uptake, exercise tolerance, and resting cardiac function, in the absence of adjuvant therapy or comorbidities, had not been investigated.
Does untreated breast cancer reduce maximal oxygen uptake, exercise tolerance, and cardiac function in a rat model?
Does untreated breast cancer reduce maximal oxygen uptake, exercise tolerance, and cardiac function in a rat model?
Absolute Event Rate: 70% vs 72.1%
p-value: p=>0.05
Untreated breast cancer in a rat model significantly reduces exercise tolerance without impairing maximal oxygen uptake or resting cardiac function, suggesting intrinsic skeletal muscle dysfunction.
May indicate non-cardiac drivers of exercise intolerance in cancer; leaves open human translation.
Breast cancer patients' maximal O 2 uptake (V 2 max) values average 60-80% of age-predicted values which is often attributed to adjuvant therapy rather than risk factors, comorbidities, or the tumor and associated factors (e.g., pro-inflammatory cytokines).It is crucial to understand the physiological mechanisms behind exercise intolerance in breast cancer patients to enhance targeted interventions; however, the effect of breast cancer, as an isolated condition on V 2 max, exercise tolerance, and resting cardiac function has not been investigated.We hypothesized that breast cancer, in the absence of underlying conditions or chemotherapy, would lower V 2 max, exercise tolerance, and cardiac function in proportion to tumor mass.Female Fischer-344 rats (~6-8 months, n = 8) were acclimatized to treadmill running for 5 days at 25 m/min for 5 min/day.To measure V 2 max, rats were placed within a plexiglass metabolic chamber connected to CO 2 and O 2 analyzers.Tests began at 25 m/min and increased (5 m/min) until exhaustion.Cardiac function was determined by echocardiography before rats received a mammary intraductal injection of rat adenocarcinoma cells (MATBIII, 6 10 3 in 50 l saline).Tumor growth was monitored daily and ~7 days following palpation (~24 days post-injection), V 2 max and echocardiography measurements were repeated.Tumor mass and volume were 2.1 0.6 g and 1685 428 (range 256-3749) mm 3 , respectively.Body mass (217 6 vs 218 6 g), V 2 max (72.1 2.7 vs 70.0 2.8 ml/kgmin; P > 0.05), and all measures of cardiac function were unchanged following tumor formation, with no significant correlation between tumor mass and V 2 max (P > 0.05).However, time to exhaustion (376 20 vs 297 25 s), final treadmill speed (48 1 vs 42 2 m/s), distance run (209 16 vs 152 18 m), and total work (45 3 vs 32 4 mkg) were significantly reduced with tumor bearing.Contrary to our hypothesis, breast cancer did not affect V 2 max or cardiac function, but reduced exercise tolerance.
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Ramona E. Weber (2025) studied Breast cancer (n=8). Orthotopic breast cancer induction (tumor bearing) vs. Pre-breast cancer baseline was evaluated on Maximal O2 uptake (VO2max) in ml/kg·min (p=>0.05). Tumor bearing in untreated breast cancer rats did not affect maximal oxygen uptake or cardiac function, but significantly reduced exercise tolerance, including time to exhaustion.
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