Patients will be consented at the earliest available opportunity following the decision that they have surgically treatable disease and they consent to pre−operative NACRT. Consent for the study will be gained as an outpatient. At "visit 1" patients will undergo CPET, as is our current standard practice, prior to commencing neoadjuvant chemoradiotherapy. As part of the assessment, they will have pulmonary function testing (static lung volumes, lung diffusing capacity). They will then undergo 6 weeks of long course NACRT, as is standard current practice at our institution. At "visit 2", approximately four to six weeks following chemoradiotherapy another CPET test will be repeated. This is also current standard practice at our institution. Data from visit 1 and visit 2 will be compared in a paired manner. A statistician will be consulted to assess the degree of normality of the data, the statistical tests to use, and for power calculations. At no point will any treatments be postponed or changed solely for the purposes of collecting data for the research.