Fig. 3.

a Difficulty in horizon estimation due to extended zone of dysplasia adjacent to the tumour. The estimation of cut-off point of basement membrane of adjacent uninvolved mucosa is impaired. b Horizon estimation is not possible in small tumours post-biopsy which appear purely submucosal even after study of multiple deeper sections. c In cases with irregular hyperplasia of adjacent epithelium, the current AJCC guidelines do not specify whether measurement should be from the level of the tip of the submucosal papilla (yellow line) or the deepest point of the rete peg. This difference can sometimes vary by 1 mm or more. d When adjacent mucosa is very thin, depth of invasion measurements equal the tumour thickness