Prognostic subdivision of ypT3 rectal tumours according to extension beyond the muscularis propria

The subdivision of T3 in rectal carcinoma according to the depth of invasion into perirectal fat has been recommended in the TNM Supplement since 1993. This study assessed the prognostic impact of this pathological staging in tumours removed after neoadjuvant chemoradiotherapy (ypT3).

Data from patients with ypT3 rectal carcinoma (less than 12 cm from the anal verge) treated with neoadjuvant chemoradiation and total mesorectal excision were analysed. Tumour category ypT3 was subdivided into ypT3a (5 mm or less) and ypT3b (more than 5 mm), based on histological measurements of maximal tumour invasion beyond the outer border of the muscularis propria.

Important differences between ypT3a (81 patients) and ypT3b (43) were found in 5-year rates of locoregional recurrence (7 versus 18 per cent; P = 0·049), distant metastasis (20 versus 41 per cent; P = 0·002), disease-free survival (73 versus 47 per cent; P = 0·001), overall survival (79 versus 74 per cent; P = 0·036) and cancer-related survival (81 versus 74 per cent; P = 0·007). In Cox regression analyses, the ypT3 subclassification was identified as an independent prognostic factor for disease-free (ypT3b: hazard ratio (HR) 2·13, 95 per cent confidence interval 1·16 to 3·89; P = 0·014), observed (ypT3b: HR 2·02, 1·05 to 3·87; P = 0·035) and cancer-related (ypT3b: HR 2·46, 1·20 to 5·04; P = 0·014) survival. Extramural venous invasion was found to be an additional prognostic factor, but the pathological node category after chemoradiotherapy (ypN) did not influence survival.

In ypT3 rectal carcinomas, the proposed subclassification is superior to ypN in predicting prognosis.