Exercise and Lung Cancer

Lung cancer is the leading cause of cancer-related death worldwide. Since the 1980s, multiple studies and organizations have demonstrated the benefit of exercise intervention and physical activity in oncology patients. Although there is limited large-scale research regarding its benefits in lung cancer patients, engaging in exercise or physical activity has been found to be safe and is still strongly recommended. The 2018 Physical Activity Guidelines Advisory Committee Scientific report (PAGAC) concluded there is moderate evidence that engaging in moderate to vigorous exercise may reduce risk or lower incidence for several cancer types, including lung cancer. Nevertheless, there are other studies showing insufficient evidence because of smoking status as a confounding variable. ^, Most patients diagnosed with lung cancer have been described as sedentary. In fact, the PAGAC report also found moderate evidence in at least two meta-analyses that increased sitting time may lead to increased risk of lung cancer.

While the American College of Sports Medicine (ACSM) Cancer Roundtable in 2018 reported benefit of exercise and physical activity in many cancer types, the guidelines found limited evidence regarding the benefits of exercise in lung cancer, and no clear guidelines on the type and intensity of recommended exercise. Exercise intervention has been reported to work across multiple organ systems to improve cardiopulmonary fitness, offset treatment side effects, and improve health-related quality of life (HRQoL) in individuals with cancer. The American Cancer Society and ACSM recommend avoiding inactivity and suggest that patients with cancer should engage in regular physical activity; specifically, they recommend at least 150 min per week of moderate aerobic activity, or 75 min of vigorous aerobic activity, with flexibility and strength exercise two or three times per week. The 2018 ACSM guidelines further recommend that exercise prescription should be individualized by addressing health-related outcomes and accounting for special considerations in order to promote adherence and limit dropout. Thus, tailoring exercise programs for patients diagnosed with lung cancer may improve the current low adherence and high dropout rates seen in a variety of studies mainly due to prediagnosis reduced fitness level and impairments related to cancer and its treatments.

Surgery is known to be a major cause of morbidity and mortality in lung cancer, even leading to at least 25% of postoperative complications, ^, thus resulting in increased health care costs. Baseline cardiopulmonary fitness provides diagnostic and prognostic information. Peak oxygen consumption (VO _2peak ) is an independent predictor of survival, and inversely related to perioperative and postoperative complications. ^, Studies have demonstrated that VO _{2 peak} or exercise tolerance is reduced in patients with lung cancer throughout the continuum of care. ^, Since lung cancer patients with lower exercise tolerance have worse surgical outcomes, chemotherapy response, and overall survival, it will be instrumental to better understand what types of exercise programs are most beneficial for these patients.

There are multiple studies that assess physical activity among patients with cancer, while others seek to specify the benefits of exercise. To clarify, Caspersen et al. described physical activity as “a bodily movement by skeletal muscles that results in energy expenditure,” while exercise is physical activity that is planned, structured, and repetitive with the goal to obtain or maintain physical fitness.

Contributors to Decreased Exercise Capacity

Exercise tolerance or capacity is directly affected by patient's age, comorbidities, and previous exercise fitness, but the decline is accelerated by the tumor burden, its pathophysiology, and the treatment-related side effects. ^, Factors that may affect the exercise tolerance or capacity in patients with lung cancer should be evaluated when determining the best exercise setting and prescription for the individual patient (see Fig. 8.1 ).

Fig. 8.1, Factors that may affect the exercise tolerance or capacity in patients with lung cancer.

Exercise capacity, a term used to describe the physical fitness of an individual, is defined as “the maximal capacity of an individual to perform aerobic work or maximal oxygen consumption.” For patients with lung cancer, exercise capacity is typically measured by field‐based functional tests (e.g., the Six‐Minute Walk Test (6MWT)), or laboratory‐based exercise tests (e.g., cardiopulmonary exercise test to measure peak oxygen uptake (VO _₂peak ).

Baseline Fitness Level

Many patients with lung cancer do not meet the World Health Organization (WHO) exercise guidelines which recommend moderate-intensity aerobic exercise of at least 150 min per week. ^, Increased exercise capacity and physical activity levels in this patient population are associated with improved HRQoL.

Currently, in nonsmall cell lung cancer (NSCLC), 6MWT is the most frequently reported assessment of exercise capacity. Poor exercise capacity, as measured by the 6mWT, is a predictor of poor prognosis in advanced NSCLC and chronic obstructive pulmonary disease (COPD). ^,

A study by Granger et al. found that individuals with NSCLC were engaged in significantly less physical activity compared to aged-matched healthy peers. Only 60% of those diagnosed with NSCLC were meeting WHO physical activity guidelines, and had a subsequent decline in physical activity, functional capacity, and strength after diagnosis, unfortunately.

Normal Aging

There is a known normal decline in exercise capacity that occurs with aging, and concomitantly, most people diagnosed with lung cancer are over the age of 65.

Comorbidities

Many patients with lung cancer also have coexisting lung diseases, in which exercise tolerance is already reduced due to cardiopulmonary impairments. These may include preexistent smoking history, COPD, asbestos-related lung disease, pulmonary fibrosis, and cardiac disease. COPD is present concomitantly in 73% of men and 53% of women with newly diagnosed primary lung cancer.

Cancer-Related and Treatment-Related Side Effects

Lung cancer, as well as cancer treatment, can cause weight loss, anemia, pulmonary dysfunction, and dyspnea, which can further negatively impact exercise capacity. Moreover, all therapeutic management may further affect the pulmonary function.

While lung resection has the best treatment survival outcomes in early-stage lung cancer, patients continue to have worsening physical fitness, respiratory function, and quality of life after surgery. ^, The presence of a tumor mass, together with related surgical procedures, may affect the respiratory system by reducing diffusion capacity. Chemotherapy-induced anemia, radiation-induced pneumonitis, and lung resection-related impairment are frequently seen and likely contribute to dyspnea and fatigue. ^,

Most patients affected by advanced lung cancer experience cachexia (69%) or sarcopenia (47%). Sarcopenia is associated with reduced survival and is highly prevalent (47%) in patients with stage III and IV disease treated with chemotherapy. Cachexia is defined as a multifactorial syndrome characterized by an ongoing loss of skeletal mass, with or without loss of fat mass, that cannot be fully reversed by conventional nutritional support and leads to progressive functional impairment. It occurs in up to one-third of patients with stage III and IV lung cancer. Patients with lung cancer may also suffer from muscle dysfunction due to disease-related metabolic disorders and side effects of chemotherapy. Muscle mass has been shown to be a predictor of all-cause mortality.

For those undergoing treatment, impaired cardiac function may also be secondary to thoracic radiation, cardiac side effects of chemotherapy, and anemia. Chemotherapeutic agents and radiotherapy may have cardiac side effects, decreased blood cell populations, and worsened vascular function. Patients who have received >30–35 Gy exposure to the chest wall are at risk for radiation-associated heart damage which can include radiated-induced injury to the myocardium, coronary arteries, and valves, resulting in diastolic dysfunction.

All these contributors not only limit a patient's exercise capacity but can also limit their ability to participate in activities of daily living (ADLs). Quality of life is also limited by direct effects of cancer progression such as fatigue, dyspnea, weight loss, pain, as well as effects of cancer treatment, which have the potential to be barriers to exercise. ^, One-third of patients with lung cancer attribute their disease as the major limitation to performing ADLs.

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