This thesis examines factors influencing contemporary outcomes of patients managed by the South East Wales upper GI cancer network multidisciplinary team. The hypotheses tested were: PET/CT defined tumour characteristics influence outcomes of patients with oesophagogastric cancer; Centralisation of oesophagogastric cancer services improves outcomes significantly; HER2 overexpression is a poor prognostic indicator following oesophagogastric cancer resection; An involved circumferential resection margin (CRM) following oesophagectomy is an independent predictor of survival. PET/CT N stage was an independent and significant predictor of survival (p=0.022). SUVmax correlated positively and significantly with endoluminal ultrasound-defined tumour volume (Spearman’s rho=0.339, p=0.001). Centralisation increased the proportion of patients receiving potentially curative treatment by 78% (p<0.0001), reduced serious operative morbidity by 50% (p=0.062), shortened total length of hospital stay from 16 days to 13 days (p=0.024) and improved median and 1-year survival from 8.7 months and 39% to 10.8 months and 46.8% respectively (p=0.032). Centralisation was an independent and significant predictor of survival (p=0.03). HER2 overexpression and gene amplification was a predictor of poor prognosis in patients with curable oesophageal cancer (p=0.03). CRM involvement was also an indicator of poor prognosis in these patients (p<0.001). The College of American Pathologists’ criteria differentiate a higher risk group than Royal College of Pathologists’ criteria but overlook a patient group with similar poor outcomes (p<0.001).