The gold standard used to establish the accuracy of endoscopic and endosonographic staging examinations was histological examination of the endoscopically or surgically resected tumour. The histological criteria used for early oesophageal carcinoma were the WHO criteria and the Vienna classification.^25,26 Generally, the resected specimens were fixed in 4% formalin, dehydrated in gradual alcohol series, and embedded in paraffin. Serial step sections of 4 μm were cut and stained with haematoxylin and eosin and/or alcian blue, pH 2.5.

The histological assessment was carried out by experienced pathologists (MS, MV). After resection, specimens were examined with regard to tumour depth (involvement of the mucosa or submucosa)—the principal point of this study. Other histological assessment criteria were: freedom from tumour at the base and lateral margins of the specimens; degree of differentiation (grade G1, well differentiated; G2, moderately differentiated; G3, poorly differentiated); and in some cases invasion of the lymphatic vessels and veins.