Maarten van Egmond

151 General discussion 7 Methodological considerations Study population The patients included in our studies showed on average high preoperative pulmonary function and physical functioning compared to reference values (Chapter 3). Moreover, few patients with chronic obstructive pulmonary disease, diabetes mellitus type 2 and cardiovascular comorbidities were present. In that respect, our study population systematically differed from other patients with esophageal cancer undergoing surgery. Klevebro et al. 21 reported in their European multicenter cohort study of 1590 included patients that cardiorespiratory comorbidity and impaired pulmonary function were associated with postoperative complications after esophageal cancer surgery. These findings confirm the relatively healthy population included in our study and could be an explanation why no association was found between preoperative physical functioning and postoperative complications (Chapter 2). For the study described in Chapter 3 only one-third of the patients were assessed at both postoperative measurements. Loss to follow-up was mainly caused by the inability to test due to weakness or no-show. It could be argued that predominantly patients with postoperative complications or low physical fitness levels were among these patients. A detailed analysis however revealed that the patients lost to follow-up did not systematically differ in baseline characteristics and physical functioning at baseline. Despite the reported prevalence of sarcopenia of at least 57% in surgical patients with esophageal cancer, only two of the included patients (chapter 4) were detected with sarcopenia based on CT scanning. 13 The low prevalence of sarcopenia in our study population may be explained by a selection of relatively healthy patients that consented to participate in the study. However, additional analysis of patients not included in our study to rule out this potential selection bias, did not reveal additional cases. In several studies it has been proposed that there is still a lack of consensus on the best techniques to measure muscle mass and reference standards to confirm sarcopenia. 22,23 Therefore, the absence of a clear definition of sarcopenia and its diagnostic criteria may have caused an underestimation of sarcopenia in our study cohort. 14 Study design In Chapter 3 we prospectively investigated our study population from 3 months before surgery to 3 months after surgery. Measurements on physical functioning were performed 3 months and 1 day before surgery and 1 week and 3 months after surgery. All patients received neoadjuvant chemoradiation therapy in the preoperative phase of which the negative effects on physical functioning and physiological capacity are well known. 11,24 Unfortunately, we have not been able to measure our patients directly after neoadjuvant chemoradiation therapy to objectify the effects on physical functioning. However, we did not find differences in physical