Determinants of exercise intolerance in breast cancer patients prior to anthracycline chemotherapy

Mechanisms of Exercise Intolerance Across the Breast Cancer Continuum: A Pooled Analysis of Individual Patient Data

PURPOSE

The purpose of this study is to evaluate the prevalence of abnormal cardiopulmonary responses to exercise and pathophysiological mechanism(s) underpinning exercise intolerance across the continuum of breast cancer (BC) care from diagnosis to metastatic disease.

METHODS

Individual participant data from four randomized trials spanning the BC continuum ([1] prechemotherapy [n = 146], [2] immediately postchemotherapy [n = 48], [3] survivorship [n = 138], and [4] metastatic [n = 47]) were pooled and compared with women at high-risk of BC (BC risk; n = 64). Identical treadmill-based peak cardiopulmonary exercise testing protocols evaluated exercise intolerance (peak oxygen consumption; V̇O2peak) and other resting, submaximal, and peak cardiopulmonary responses. The prevalence of 12 abnormal exercise responses was evaluated. Graphical plots of exercise responses were used to identify oxygen delivery and/or uptake mechanisms contributing to exercise intolerance. Unsupervised, hierarchical cluster analysis was conducted to explore exercise response phenogroups.

RESULTS

Mean V̇O2peak was 2.78 ml O2.kg-1·min-1 (95% confidence interval [CI], -3.94, -1.62 mL O2.kg-1·min-1; P < 0.001) lower in the pooled BC cohort (52 ± 11 yr) than BC risk (55 ± 10 yr). Compared with BC risk, the pooled BC cohort had a 2.5-fold increased risk of any abnormal cardiopulmonary response (odds ratio, 2.5; 95% confidence interval, 1.2, 5.3; P = 0.014). Distinct exercise responses in BC reflected impaired oxygen delivery and uptake relative to control, although considerable inter-individual heterogeneity within cohorts was observed. In unsupervised, hierarchical cluster analysis, six phenogroups were identified with marked differences in cardiopulmonary response patterns and unique clinical characteristics.

CONCLUSIONS

Abnormal cardiopulmonary response to exercise is common in BC and is related to impairments in oxygen delivery and uptake. The identification of exercise response phenogroups could help improve cardiovascular risk stratification and guide investigation of targeted exercise interventions.

Exercise, cancer, and the cardiovascular system: clinical effects and mechanistic insights

Cardiovascular diseases and cancer are the leading causes of death in the Western world and share common risk factors. Reduced cardiorespiratory fitness (CRF) is a major determinant of cardiovascular morbidity and cancer survival. In this review we discuss cancer- induced disturbances of parenchymal, cellular, and mitochondrial function, which limit CRF and may be antagonized and attenuated through exercise training. We show the impact of CRF on cancer survival and its attenuating effects on cardiotoxicity of cancer-related treatment. Tailored exercise programs are not yet available for each tumor entity as several trials were performed in heterogeneous populations without adequate cardiopulmonary exercise testing (CPET) prior to exercise prescription and with a wide variation of exercise modalities. There is emerging evidence that exercise may be a crucial pillar in cancer treatment and a tool to mitigate cardiotoxic treatment effects. We discuss modalities of aerobic exercise and resistance training and their potential to improve CRF in cancer patients and provide an example of a periodization model for exercise training in cancer.

Determinants of Impaired Peak Oxygen Uptake in Breast Cancer Survivors: JACC: CardioOncology Primer

•Exercise intolerance is common among breast cancer survivors.•Exercise intolerance in breast cancer survivors is related to cardiac, vascular, and skeletal muscle impairments.•Holistic rehabilitation or pharmacological therapies are needed to address these impairments.

How do practitioners prescribe exercise to patients with breast cancer? Professional perspectives on the key considerations for aerobic exercise in patients with breast cancer undergoing chemotherapy

OBJECTIVES

This study aimed to understand the key factors experienced accredited exercise physiologists (AEPs) and medical professionals consider when prescribing/recommending aerobic exercise to patients with breast cancer undergoing chemotherapy.

DESIGN

Modified Delphi Survey.

METHODS

A four-round, two-phase survey was conducted. Following a Delphi approach, four cancer-specific AEPs, four oncologists, and one breast cancer surgeon (median 13-yr breast-cancer-specific experience) completed phase one. Eighty-four AEPs (median 5-yr experience) completed phase two. Phase one participants answered open- and close-ended questions regarding key considerations for aerobic exercise in patients with breast cancer undergoing chemotherapy, and what information should be collected to guide exercise prescription. All questions and considerations agreed upon in phase one (>70 % rating 7-9 on a 0-9 Likert Scale) were rated by AEPs in phase two.

RESULTS

Key considerations for exercise assessment and prescription aligned closely with exercise guidelines for cancer survivors. Common strategies for exercise individualisation were identified by AEPs, including separating aerobic exercise into 5-to--9-minute bouts when required and avoiding exercising to complete exhaustion. Exercise intensity and duration should be adjusted throughout chemotherapy to improve tolerance and adherence. Novel considerations for subjective questioning and objective assessments to tailor exercise prescription were outlined.

CONCLUSIONS

This study identifies how professionals approach exercise assessment and prescription in patients with breast cancer undergoing chemotherapy. Findings can guide AEPs in practice when prescribing tailored exercise to breast cancer patients undergoing chemotherapy and inform future guidelines.

Cardiac mechanisms for low aerobic power in anthracycline treated, older, long-term breast cancer survivors

Breast cancer survivors have reduced peak aerobic capacity (VO_2peak) which may be related to latent or lingering chemotherapy induced cardiac damage. Nine, older (67 ± 3 years), long-term survivors (9.8 years) of anthracycline based chemotherapy and age- and sex-matched healthy controls were recruited and tested to determine whether: i) VO_2peak remains reduced in long-term survivorship; and ii) reductions in VO_2peak are due to cardiac dysfunction. VO_2peak was significantly reduced in breast cancer survivors relative to healthy controls (15.9 ± 2.0 vs 19.9 ± 3.1 ml/kg/min, p = 0.006), however the heart rate and stroke volume responses to exercise were normal (heart rate reserve; 88 ± 9 vs 85 ± 10 bpm, p = 0.62: stroke volume reserve; 13 ± 6 vs 13 ± 9 ml,p = 0.94). These findings indicate low-normal ventricular size in long-term breast cancer survivors, but normal reserve function.

Breast cancer survivors with preserved or rescued cardiorespiratory fitness have similar cardiac, pulmonary and muscle function compared to controls

Breast cancer survivors (BCS) have a high prevalence of cardiovascular disease and low cardiorespiratory fitness (CRF). CRF is an important predictor of survival in BCS. However, the physiological factors that contribute to low CRF in BCS have not been completely elucidated. To assess differences in physiological factors (cardiac, pulmonary, muscle function) related to CRF between BCS and controls. Twenty-three BCS and 23 age-body mass index (BMI) matched controls underwent a peak cycling exercise test to determine CRF, with physiological factors measured at resting and at peak exercise. Cardiac hemodynamics (stroke volume [SV], SVindex, heart rate [HR], cardiac output [Formula: see text], and [Formula: see text]index) were evaluated using ultrasonography. Pulmonary function was evaluated using the oxygen uptake efficiency slope (OUES), ventilation to carbon dioxide production slope [Formula: see text] and breathing reserve at peak exercise (BR). Muscle oxygenation variables (oxygenated [HbO₂] deoxygenated [HHb] and total hemoglobin [Hb], and tissue oxygenation index [TSI]) were measured with near-infrared spectroscopy (NIRS). Both groups had similar CRF and similarly increased all hemodynamic variables (HR, SV, SVindex, [Formula: see text] and [Formula: see text]index) at peak exercise compared to resting (p < 0.001). BCS had higher overall HR and lower SVindex (group effect, p < 0.05). BCS had similar OUES, [Formula: see text] and BR compared to the controls. Both groups decreased TSI, and increased Hb and HHb similarly at peak exercise compared to resting (p < 0.001). Our data suggest BCS do not exhibit differences in cardiac, pulmonary, or muscle function at peak exercise compared to controls, when both groups have similar CRF and physical activity.

Rethinking Rehabilitation: A REVIEW OF PATIENT POPULATIONS WHO CAN BENEFIT FROM CARDIAC REHABILITATION

Although cardiac rehabilitation (CR) is safe and highly effective for individuals with various cardiovascular health conditions, to date there are only seven diagnoses or procedures identified by the Centers for Medicare & Medicaid Services that qualify for referral. When considering the growing number of individuals with cardiovascular disease (CVD), or other health conditions that increase the risk for CVD, it is important to determine the extent for which CR could benefit these populations. Furthermore, there are some patients who may currently be eligible for CR (spontaneous coronary artery dissection, left ventricular assistant device) but make up a relatively small proportion of the populations that are regularly attending and participating. Thus, these patient populations and special considerations for exercise might be less familiar to professionals who are supervising their programs. The purpose of this review is to summarize the current literature surrounding exercise testing and programming among four specific patient populations that either do not currently qualify for (chronic and end-stage renal disease, breast cancer survivor) or who are eligible but less commonly seen in CR (sudden coronary artery dissection, left ventricular assist device). While current evidence suggests that individuals with these health conditions can safely participate in and may benefit from supervised exercise programming, there is an immediate need for high-quality, multisite clinical trials to develop more specific exercise recommendations and support the inclusion of these populations in future CR programs.

Thermoregulation is not impaired in breast cancer survivors during moderate-intensity exercise performed in warm and hot environments

This study aimed to assess how female breast cancer survivors (BCS) respond physiologically, hematologically, and perceptually to exercise under heat stress compared to females with no history of breast cancer (CON). Twenty-one females (9 BCS and 12 CON [age; 54 ± 7 years, stature; 167 ± 6 cm, body mass; 68.1 ± 7.62 kg, and body fat; 30.9 ± 3.8%]) completed a warm (25℃, 50% relative humidity, RH) and hot (35℃, 50%RH) trial in a repeated-measures crossover design. Trials consisted of 30 min of rest, 30 min of walking at 4 metabolic equivalents, and a 6-minute walk test (6MWT). Physiological measurements (core temperature (Tre ), skin temperature (Tskin ), heart rate (HR), and sweat analysis) and perceptual rating scales (ratings of perceived exertion, thermal sensation [whole body and localized], and thermal comfort) were taken at 5- and 10-min intervals throughout, respectively. Venous blood samples were taken before and after to assess; IL-6, IL-10, CRP, IFN-γ, and TGF-β1 . All physiological markers were higher during the 35 versus 25℃ trial; Tre (~0.25℃, p = 0.002), Tskin (~3.8℃, p < 0.001), HR (~12 beats·min-1 , p = 0.023), and whole-body sweat rate (~0.4 L·hr-1 , p < 0.001), with no difference observed between groups in either condition (p > 0.05). Both groups covered a greater 6MWT distance in 25 versus 35℃ (by ~200 m; p = 0.003). Nevertheless, the control group covered more distance than BCS, regardless of environmental temperature (by ~400 m, p = 0.03). Thermoregulation was not disadvantaged in BCS compared to controls during moderate-intensity exercise under heat stress. However, self-paced exercise performance was reduced for BCS regardless of environmental temperature.

Vo2peak in Adult Survivors of Hodgkin Lymphoma: Rate of Decline, Sex Differences, and Cardiovascular Events

Background

Adult survivors of Hodgkin lymphoma (HL) are at increased risk of cardiovascular (CV) events secondary to mediastinal radiation therapy (RT).

Objectives

In this group of patients, we assessed the association between cardiopulmonary exercise testing (CPET), as determined by percent-predicted peak Vo₂ (ppVo₂peak), and clinical outcomes, as well as the rate of ppVo₂peak decline and sex differences.

Methods

All survivors of HL who were >10 years post chest RT and who underwent ≥1 CPET were enrolled from a single center. Traditional CV and treatment risk factors, along with CV events, were ascertained.

Results

A total of 64 patients (67% female; median age 51 years [range 26 to 70 years]) with a median follow-up time after RT of 23 years (range 11 to 41 years), and 141 CPET studies, were included. Median initial ppVo₂peak was 91% (range 58% to 138%). ppVo₂peak in survivors declined by 7.5 percentage points every 10-year period after RT, as compared with age- and sex-based norms (P = 0.001), even after adjusting for hypertension and history of anthracycline. Both male and female patients had a similar rate of ppVo₂peak decline. However, women had a lower ppVo₂peak at all times, and they developed abnormal ppVo₂peak (≤85%) on average earlier than men (24.1 years vs 47.0 years after RT). Patients with abnormal ppVo₂peak vs normal ppVo₂peak (>85%), had an increased risk of CV events (59% vs 16%). Abnormal ppVo₂peak was independently associated with the risk of CV events (adjusted HR: 6.37; 95% CI: 2.06-19.80; P = 0.001).

Conclusions

Percent-predicted Vo₂peak in long-term survivors of HL who were treated with chest RT progressively declined as compared with population- and sex-based norms. Importantly, women developed abnormal ppVo₂peak more than 2 decades earlier than male survivors. Abnormal ppVo₂peak was associated with an increased risk of CV events in this group of patients.

The Australia and New Zealand Cardio-Oncology Registry: evaluation of chemotherapy-related cardiotoxicity in a national cohort of paediatric cancer patients

Cancer therapy related cardiac dysfunction (CTRCD) is an area of increasing focus, particularly during the survivorship period, for paediatric, adolescent and adult cancer survivors. With the advent of immunotherapy and targeted therapy, there is a new set of mechanisms from which paediatric and young adult patients with cancer may suffer cardiovascular injury. Furthermore, cardiovascular disease is the leading cause of morbidity and mortality in the survivorship period. The recently established Australian Cardio-Oncology Registry is the largest and only population-based cardiotoxicity database of paediatric and adolescent and young adult oncology patients in the world, and the first paediatric registry that will document cardiotoxicity caused by chemotherapy and novel targeted therapies using a prospective approach. The database is designed for comprehensive data collection and evaluation of the Australian practice in terms of diagnosis and management of CTRCD. Using the Australian Cardio-Oncology Registry critical clinical information will be collected regarding predisposing factors for the development of CTRCD, the rate of subclinical left ventricular dysfunction and transition to overt heart failure, further research into protectant molecules against cardiac dysfunction and aid in the discovery of which genetic variants predispose to CTRCD. A health economic arm of the study will assess the cost/benefit of both the registry and cardio-oncology clinical implementation. Finally, an imaging arm will establish if exercise cardiac magnetic resonance imaging and VO₂ max testing is a more sensitive predictor of cardiac reserve in paediatric and adolescent and young adult oncology patients exposed to cardiac toxic therapies.

Exercise Cardiovascular Magnetic Resonance: A Review

While pharmacologic stress cardiovascular magnetic resonance imaging (MRI) is a robust noninvasive tool in the diagnosis and prognostication of epicardial coronary artery disease, clinical guidelines recommend exercise-based testing in those patients who can exercise. This review describes the development of exercise cardiovascular MRI protocols, summarizes the insights across various patient populations, and highlights future research initiatives. LEVEL OF EVIDENCE: 5 TECHNICAL EFFICACY: Stage 2.

High intensity exercise during breast cancer chemotherapy - effects on long-term myocardial damage and physical capacity - data from the OptiTrain RCT

BACKGROUND

Adjuvant systemic breast cancer treatment improves disease specific outcomes, but also presents with cardiac toxicity. In this post-hoc exploratory analysis of the OptiTrain trial, the effects of exercise on cardiotoxicity were monitored by assessing fitness and biomarkers over the intervention and into survivorship. Methods; Women starting chemotherapy were randomized to 16-weeks of resistance and high-intensity interval training (RT-HIIT), moderate-intensity aerobic and high-intensity interval training (AT-HIIT), or usual care (UC). Outcome measures included plasma troponin-T (cTnT), Nt-pro-BNP and peak oxygen uptake (VO_2peak), assessed at baseline, post-intervention, and at 1- and 2-years.

RESULTS

For this per-protocol analysis, 88 women met criteria for inclusion. Plasma cTnT increased in all groups post-intervention. At the 1-year follow-up, Nt-pro-BNP was lower in the exercise groups compared to UC. At 2-years there was a drop in VO_2peak for patients with high cTnT and Nt-pro-BNP. Fewer patients in the RT-HIIT group fulfilled biomarker risk criteria compared to UC (OR 0.200; 95% CI = 0.055-0.734).

CONCLUSIONS

In this cohort, high-intensity exercise was associated with lower levels of NT-proBNP 1-year post-baseline, but not with cTnT directly after treatment completion. This may, together with the preserved VO_2peak in patients with low levels of biomarkers, indicate a long-term cardioprotective effect of exercise.

TRIAL REGISTRATION

Clinicaltrials. govNCT02522260 , Registered 13th of august 2015 - Retrospectively Registered.

Long-term Cardiopulmonary Consequences of Treatment-Induced Cardiotoxicity in Survivors of ERBB2-Positive Breast Cancer

Importance

Trastuzumab improves outcomes in patients with ERBB2-positive (formerly HER2) breast cancer but is associated with treatment-induced cardiotoxicity, most commonly manifest by an asymptomatic decline in left ventricular ejection fraction (LVEF). Little is known to date regarding the long-term effects of treatment-induced cardiotoxicity on cardiopulmonary function in patients who survive trastuzumab-treated breast cancer.

Objective

To determine whether treatment-induced cardiotoxicity recovers or is associated with long-term cardiopulmonary dysfunction in survivors of ERBB2-positive breast cancer.

Design, Setting, and Participants

This cross-sectional case-control study enrolled patients with nonmetastatic ERBB2-positive breast cancer after completion of trastuzumab-based therapy (median, 7.0 [interquartile range (IQR), 6.2-8.7] years after therapy) who met 1 of 2 criteria: (1) cardiotoxicity (TOX group) developed during trastuzumab treatment (ie, asymptomatic decrease of LVEF≥10% from baseline to <55% [n = 22]) or (2) no evidence of cardiotoxicity during trastuzumab treatment (NOTOX group [n = 20]). Patients were treated at the Memorial Sloan Kettering Cancer Center. Fifteen healthy control participants (HC group) were also enrolled for comparison purposes. All groups were frequency matched by age strata (<55, 55-64, and ≥65 years). Data were collected from September 9, 2016, to August 10, 2018, and analyzed from November 20, 2018, to August 12, 2019.

Main Outcomes and Measures

Speckle-tracking echocardiography and maximal cardiopulmonary exercise testing were performed to measure indices of left ventricular function (including LVEF and global longitudinal strain [GLS]) and peak oxygen consumption (peak VO2).

Results

A total of 57 participants (median age, 60.8 [IQR, 52.7-65.7] years) were included in the analysis. Overall, 38 of 42 patients with breast cancer (90%) were treated with anthracyclines before trastuzumab. Resting mean (SD) LVEF was significantly lower in the TOX group (56.9% [5.2%]) compared with the NOTOX (62.4% [4.0%]) and HC (65.3% [2.9%]) groups; similar results were found for GLS (TOX group, -17.8% [2.2%]; NOTOX group, -19.8% [2.2%]; HC group, -21.3% [1.8%]) (P < .001). Mean peak VO2 in the TOX group (22.9 [4.4] mL/kg/min) was 15% lower compared with the NOTOX group (27.0 [5.3] mL/kg/min; P = .03) and 25% lower compared with the HC group (30.5 [3.4] mL/ kg/min; P < .001). In patients with breast cancer, GLS was significantly associated with peak VO2 (β coefficient, -0.75; 95% CI, -1.32 to -0.18).

Conclusions and Relevance

Treatment-induced cardiotoxicity appears to be associated with long-term marked impairment of cardiopulmonary function and may contribute to increased risk of late-occurring cardiovascular disease in survivors of ERBB2-positive breast cancer.

Sodium nitrate co-supplementation does not exacerbate low dose metronomic doxorubicin-induced cachexia in healthy mice

The purpose of this study was to determine whether (1) sodium nitrate (SN) treatment progressed or alleviated doxorubicin (DOX)-induced cachexia and muscle wasting; and (2) if a more-clinically relevant low-dose metronomic (LDM) DOX treatment regimen compared to the high dosage bolus commonly used in animal research, was sufficient to induce cachexia in mice. Six-week old male Balb/C mice (n = 16) were treated with three intraperitoneal injections of either vehicle (0.9% NaCl; VEH) or DOX (4 mg/kg) over one week. To test the hypothesis that sodium nitrate treatment could protect against DOX-induced symptomology, a group of mice (n = 8) were treated with 1 mM NaNO₃ in drinking water during DOX (4 mg/kg) treatment (DOX + SN). Body composition indices were assessed using echoMRI scanning, whilst physical and metabolic activity were assessed via indirect calorimetry, before and after the treatment regimen. Skeletal and cardiac muscles were excised to investigate histological and molecular parameters. LDM DOX treatment induced cachexia with significant impacts on both body and lean mass, and fatigue/malaise (i.e. it reduced voluntary wheel running and energy expenditure) that was associated with oxidative/nitrostative stress sufficient to induce the molecular cytotoxic stress regulator, nuclear factor erythroid-2-related factor 2 (NRF-2). SN co-treatment afforded no therapeutic potential, nor did it promote the wasting of lean tissue. Our data re-affirm a cardioprotective effect for SN against DOX-induced collagen deposition. In our mouse model, SN protected against LDM DOX-induced cardiac fibrosis but had no effect on cachexia at the conclusion of the regimen.

Cardiopulmonary exercise testing - refining the clinical perspective by combining assessments

INTRODUCTION

Cardiorespiratory fitness (CRF) is now established as a vital sign. Cardiopulmonary exercise testing (CPX) is the gold-standard approach to assessing CRF.

AREAS COVERED

A body of literature spanning several decades clearly supports the clinical utility of CPX in those who are apparently health and at risk for chronic disease as well as numerous patient populations. While CPX, in and of itself, is a valid and reliable clinical assessment, combining findings with other available assessments may provide a more comprehensive perspective that enhances clinical decision making and outcomes. The current review will accomplish the following: (1) define key CPX measures based upon current evidence; and (2) describe the current evidence addressing the relationships between CPX and echocardiography, serum biomarkers, and cardiovascular magnetic resonance.

EXPERT OPINION

Cardiopulmonary exercise testing provides prognostic and diagnostic information in apparently healthy individuals, those at risk for one or more chronic conditions, as well as numerous patient populations. Moreover, if the goal of an intervention is to improve one or more systems integral to the physiologic response to exercise, CPX should be considered as a central assessment to gauge therapeutic efficacy. To further refine the information obtained from CPX, combining other assessments has demonstrated promise.

Cardiovascular Consequences of Skeletal Muscle Impairments in Breast Cancer

Breast cancer survivors suffer from disproportionate cardiovascular disease risk compared to age-matched controls. Beyond direct cardiotoxic effects due to treatments such as chemotherapy and radiation, breast-cancer-related reductions in skeletal muscle mass, quality and oxidative capacity may further contribute to cardiovascular disease risk in this population by limiting the ability to engage in aerobic exercise—a known promoter of cardiovascular health. Indeed, 20–30% decreases in peak oxygen consumption are commonly observed in breast cancer survivors, which are indicative of exercise intolerance. Thus, breast-cancer-related skeletal muscle damage may reduce exercise-based opportunities for cardiovascular disease risk reduction. Resistance training is a potential strategy to improve skeletal muscle health in this population, which in turn may enhance the capacity to engage in aerobic exercise and reduce cardiovascular disease risk.

Exercise Intolerance in Anthracycline-Treated Breast Cancer Survivors: The Role of Skeletal Muscle Bioenergetics, Oxygenation, and Composition

BACKGROUND

Peak oxygen consumption (VO2 ) is reduced in women with a history of breast cancer (BC). We measured leg blood flow, oxygenation, bioenergetics, and muscle composition in women with BC treated with anthracycline chemotherapy (n = 16, mean age: 56 years) and age- and body mass index-matched controls (n = 16).

MATERIALS AND METHODS

Whole-body peak VO2 was measured during cycle exercise. 31 Phosphorus magnetic resonance (MR) spectroscopy was used to measure muscle bioenergetics during and after incremental to maximal plantar flexion exercise (PFE). MR imaging was used to measure lower leg blood flow, venous oxygen saturation (Sv O2 ), and VO2 during submaximal PFE, and abdominal, thigh, and lower leg intermuscular fat (IMF) and skeletal muscle (SM).

RESULTS

Whole-body peak VO2 was significantly lower in BC survivors versus controls (23.1 ± 7.5 vs. 29.5 ± 7.7 mL/kg/minute). Muscle bioenergetics and mitochondrial oxidative capacity were not different between groups. No group differences were found during submaximal PFE for lower leg blood flow, Sv O2 , or VO2 . The IMF-to-SM ratio was higher in the thigh and lower leg in BC survivors (0.36 ± 0.19 vs. 0.22 ± 0.07, p = .01; 0.10 ± 0.06 vs. 0.06 ± 0.02, p = .03, respectively) and were inversely related to whole-body peak VO2 (r = -0.71, p = .002; r = -0.68, p = .003, respectively). In the lower leg, IMF-to-SM ratio was inversely related to VO2 and O2 extraction during PFE.

CONCLUSION

SM bioenergetics and oxidative capacity in response to PFE are not impaired following anthracycline treatment. Abnormal SM composition (increased thigh and lower leg IMF-to-SM ratio) may be an important contributor to reduced peak VO2 during whole-body exercise among anthracycline-treated BC survivors.

IMPLICATIONS FOR PRACTICE

Peak oxygen consumption (peak VO2 ) is reduced in breast cancer (BC) survivors and is prognostic of increased risk of cardiovascular disease-related and all-cause mortality. Results of this study demonstrated that in the presence of deficits in peak VO2 1 year after anthracycline therapy, skeletal muscle bioenergetics and oxygenation are not impaired. Rather, body composition deterioration (e.g., increased ratio of intermuscular fat to skeletal muscle) may contribute to reduced exercise tolerance in anthracycline BC survivors. This finding points to the importance of lifestyle interventions including caloric restriction and exercise training to restore body composition and cardiovascular health in the BC survivorship setting.

Effects of Exercise Therapy Dosing Schedule on Impaired Cardiorespiratory Fitness in Patients With Primary Breast Cancer: A Randomized Controlled Trial

BACKGROUND

Current exercise guidelines for clinical populations recommend an exercise therapy (ET) prescription of fixed intensity (moderate), duration (40-50 minutes per session), and volume (120-160 min/wk). A critical overarching element of exercise programming that has received minimal attention is dose scheduling. We investigated the tolerability and efficacy of 2 exercise training dose regimens on cardiorespiratory fitness and patient-reported outcomes in patients with posttreatment primary breast cancer.

METHODS

Using a parallel-group randomized trial, we randomly allocated 174 postmenopausal patients (2.8 years after adjuvant therapy) with impaired peak oxygen consumption (VO₂peak) to 1 of 2 supervised exercise training interventions delivered with a standard linear (LET) (fixed dose intensity per session for 160 min/wk) or nonlinear (NLET) (variable dose intensity per session for ≈120 min/wk) schedule compared with a stretching attention control group for 16 consecutive weeks. Stretching was matched to exercise dosing arms on the basis of location, frequency, duration, and treatment length. The primary end point was change in VO₂peak (mL O₂·kg^-1·min^-1) from baseline to after intervention. Secondary end points were patient-reported outcomes, tolerability, and safety.

RESULTS

No serious adverse events were observed. Mean attendance was 64%, 75%, and 80% for attention control, LET, and NLET, respectively. In intention-to-treat analysis, VO₂peak increased 0.6±1.7 mL O₂·kg^-1·min^-1 (P=0.05) and 0.8±1.8 mL O₂·kg^-1·min^-1 (P=0.07) in LET and NLET, respectively, compared with attention control. Change in VO₂peak ranged from -2.7 to 4.1 mL O₂·kg^-1·min^-1 and from -3.6 to 5.1 mL O₂·kg^-1·min^-1 in LET and NLET, respectively. Approximately 40% of patients in both exercise dosing regimens were classified as VO₂peak responders (ie, Δ ≥1.32 mL O₂·kg^-1·min^-1). NLET improved all patient-reported outcomes compared with attention control.

CONCLUSIONS

Short-term exercise training, independently of dosing schedule, is associated with modest improvements in cardiorespiratory fitness in patients previously treated for early-stage breast cancer.

CLINICAL TRIAL REGISTRATION

URL: https://www.clinicaltrials.gov. Unique identifier: NCT01186367.