Clinical significance of pT sub-classification in surgical pathology of colorectal cancer

Tumour stage is the strongest prognostic parameter in colorectal cancer. The study aimed to evaluate the prognostic impact of pT2, pT3, and pT4 sub-classification. Three hundred eighty-one surgical colorectal cancer specimens were retrospectively re-evaluated. pT2 tumours were sub-classified according to infiltration of the inner circumferential (pT2a) or outer longitudinal (pT2b) layer of the muscularis propria. pT3 tumours were sub-classified by measuring the maximal tumour invasion beyond the outer border of the muscularis propria (pT3a a parts per thousand currency signaEuro parts per thousand 1 mm, pT3b > 1-5 mm, pT3c > 5-15 mm, and pT3d > 15 mm). pT4 tumours were sub-classified according to invasion of other organs or structures (pT4a) or perforation of the visceral peritoneum (pT4b). Data were correlated with other pathological parameters and patient outcome. Seventy pT2 tumours were re-classified as 37 pT2a and 33 pT2b tumours. There was no significant association with tumour grade, angioinvasion, or lymph node involvement and no significant impact on prognosis. Two hundred eighteen pT3 tumours were re-classified as 49 pT3a, 83 pT3b, 53 pT3c, and 33 pT3d tumours. pT3 sub-classification was significantly associated with tumour grade, angioinvasion, and lymph node involvement and proved to be an independent prognostic variable with respect to progression-free and cancer-specific survival. A cut-off level of 5 mm is recommended. Sixty-five pT4 tumours were re-classified as 15 pT4a and 50 pT4b tumours. There was no significant association with tumour grade, angioinvasion, or lymph node involvement and no significant impact on prognosis. pT3 sub-classification was significantly associated with patient outcome. In contrast, pT2 and pT4 sub-classification did not show clinical significance.