Introduction
Cancer is the leading cause of death in people aged 40–79 years and is overall the second leading cause of death in the United States.
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Among all the cancer types, lung cancer is the main cause of cancer-related mortality. It is estimated that in the United States, 224,210 new cases of lung cancer were diagnosed and 159,260 deaths occurred in 2014 alone. Lung cancer causes more deaths than those from the next three most common types of cancers, such as colorectal, breast, and pancreatic cancers, combined together.
More than half of all lung cancer patients at the time of diagnosis have stage IV disease that has a 5-year survival rate <5%.1 Cachexia is a wasting syndrome seen not only in cancer but also in chronic obstructive pulmonary disease,2 chronic heart failure,3 and acquired immune deficiency syndrome.4
Cancer cachexia is defined as a multifactorial syndrome characterized by an ongoing loss of skeletal muscle mass (with or without loss of fat mass) that cannot be fully reversed by conventional nutrition support and leads to progressive functional impairment.5
The incidence of cachexia varies with tumor type, being lowest in sarcoma and breast cancers, whereas 80%–90% of patients with pancreatic and gastric cancers experience weight loss.6 It is estimated that 60% of lung cancer patients have cancer cachexia.7 The different incidence of cachexia among various cancer types may be explained by differing biology of the tumor.
The variability in the estimation of cachexia among cancer patients has also been due to lack of a consensus clinical definition for cancer cachexia.8
Recently, various definitions of cachexia have been proposed including weight loss >5% of body weight or body mass index (BMI) <20 kg/m2 (where weight loss is not available) along with the presence of fatigue, anorexia, decreased muscle strength, low fat-free mass index, and abnormal biochemistry.9
In another definition and classification of cancer-specific cachexia, a proposal by the SCRINIO (screening of the nutrition risk of 1307 oncology patients) working group, cachexia was defined as ≥10% loss of body weight in the setting of underlying malignancy.10
More recently, an international consensus definition and classification of cancer cachexia were proposed. Cancer cachexia was defined as weight loss of >5% in the preceding 6 months or >2% in individuals showing depletion based on BMI (<20 kg/m2) and sarcopenia.5
Cancer cachexia is also described as a continuum, with three stages of clinical relevance: pre-cachexia, cachexia, and refractory cachexia depending on the degree of weight loss, sarcopenia, and shortened expected survival.
