1. THE SIGNIFICANCE OF HISTOLOGICAL SUBSTAGING IN CURATIVE RESECTED T3 COLORECTAL CANCER Karl Mrak & Jörg Tschmelitsch Department of Surgery, Barmherzige Brüder Hospital St. Veit/Glan, Austria BACKGROUND Depth of infiltration of bowel wall is an important prognostic factor in colo-rectal malignancies. Several studies have shown, that the pT-stage according to UICC/AJCC influences lymph node involvement, vessel invasion, recurrence and long-term survival. However there is few data about the role of subgroups within pT-stages particularly in pT3-tumors. The aim of our study was to evaluate whether depth of infiltration within T3 colorectal tumors influences long term oncologic outcome. MATERIAL AND METHODS Patients with pT3, N-/+, M0 colon or rectal cancer who underwent curative (R0) resection at our department between January 1991 and December 2003 were collected in a prospectively maintained cancer database. For our analysis additional pathologic examinations according to TNM supplement published by Hermanek P. et al in 1993 were performed and four subgroups, a through d, based on depth of microscopic penetration into the subserosa were categorized (Figure 1). The influence on local recurrence and/or distant metastasis as well as overall and disease-free survival was tested for each subgroup and compared in an univariate and multivariate analysis. Measuring the maximal tumour invasion beyond the outer border of the muscularis propria pT3a ≤ 1 mm pT3b > 1-5 mm pT3c > 5-15 mm pT3d > 15 mm pT3 SUBCLASSIFICATION Mucosa Submucosa M. propria Subserosa Serosa Figure 1 RESULTS Overall 368 patients were evaluated with a median age of 69 years (range 32 – 92) and a median follow-up time of 92.5 months (range 0 – 196). In 181 patients with colon cancer 5- and 10 years overall survival was 82.7% and 65.0%; 5- and 10 years disease free survival was 80.9% and 64.4%. For 187 rectal cancer patients 5- and 10 years overall survival was 69.0% and 50.5%; 5- and 10 years disease free survival was 61.3% and 47.5%. The survival rates for pT3 subgroups are shown in Figure 2-5. Neither in colon nor in rectal cancer different pT3 subgroups showed a statistical significant influence on survival or the occurrence of local or distant recurrence in univariate and multivariate analyses. However there was a significant influence of higher pT3 subgroups on lymph node involvement and vessel invasion in rectal cancer patients. CONCLUSIONS  Subdivision of pT3 tumors in colon cancer, based on depth of infiltration does not provide us with additional information about prognosis.  In rectal cancer T3 – substages were associated with lymph node involvement, however we could not show an impact on recurrence or survival.  According to our results in patients with T3 colorectal cancer, prognosis or treatment decisions cannot be based on pathologic substaging by depth of infiltration. LITERATURE 1. Hermanek P, Henson DE, Hutter RVP, Sobin LH, eds. International Union Against Cancer (UICC): TNM Supplement 1993. A commentary on uniform use. Berlin, Heidelberg, New York. Springer Verlag; 1993: 122. Overall Survival Percentages (Colon) 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Survival Time [month] 0102030405060708090100120140160180 pT class3A3B3C3D Disease Free Survival Percentages (Colon ) 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Survival Time [month] 0102030405060708090100110120130140150160170180190200 pT class3A3B3C3D