Maarten van Egmond

76 Chapter 4 One of the main reasons for this low amount of sarcopenic patients could be that we only analyzed patients in this study that agreed to have their muscle strength measured preoperatively. This group of included patients (N = 125) was smaller than the total amount of patients that was indicated for curative-intent surgery (N = 226). That could have caused a selection of relatively healthy patients. However, additional analysis of the patients not included in this study showed no additional cases of sarcopenia. Second, there are still concerns in the conceptualization of sarcopenia leading to various definitions and cut-off values, which may have led to an underestimation of sarcopenic patients in this study cohort. 37 Recent research suggested that not only changes in skeletal muscle mass, but also ectopic fat infiltration in skeletal muscle (myosteatosis) negatively affects muscle function and seems to interact with sarcopenia. However, with CT it is not possible to directly measure the lipid content or detect the location of intramyocellular and extramyocellular fat tissue. 35 Third, while each variable was independently associated with muscle mass, there is still 34% of the variability unexplained. Besides the lack of physical activity and muscle strength, also protein metabolism and nutrition explain the loss of muscle mass. 36 Prolonged metabolism due to aggressive tumor biology leads to systemic inflammation and consecutively to muscle wasting. 38 We did not take these mechanisms into account in this study and should be subject of further studies.