TN categorization for rectal and colon cancers based on national survival outcome data

Abstract

4020 Background: The 6th edition (ed) of AJCC staging subdivided Stage II into IIA(T3N0)/IIB(T4N0) and Stage III into IIIA(T1–2N1M0), IIIB(T3–4N1M0), IIIC(anyTN2M0). Subsequent analyses supported further substaging of Stage III due to improved survival with T1–2N2 cancers. Before making such changes in the AJCC 7th ed, the HTF sought validation in a population-based dataset that depth of invasion interacts with nodal status to affect survival. Methods: SEER population-based data from Jan 1, 1992 to Dec 2004 for 35,829 rectal and 109,953 colon cancer pts was compared to Cooperative Group rectal data on 2551 pts (Rectal Pooled Analysis). Tumors were stratified by SEER’s ‘extent of disease’ and ‘number of positive nodes’ coding schemes. T4N0 cancers were stratified by ‘tumors that perforate visceral peritoneum’ vs ‘tumors that invade or are adherent to adjacent organs or structures’. N1 and N2 were stratified by number of N+: N1(1 vs 2–3), N2(4–6 vs >7). Observed 5-y survival (∼ overall survival, OS) was obtained for each TN category. Results: Survival outcomes for rectal and colon cancer were similar by TN category (Table). T1–2N2 cancers have better prognosis than T3–4N2, and T4bN1 lesions have prognosis similar to T4N2 in both rectal and colon datasets. Prognosis for T4a lesions (Tumor penetrates visceral peritoneum) is better than T4b(Tumor directly invades or is adherent to other organs or structures) by N category (Table,N0/N1). Number of N+ affects prognosis. N1a(1N+) has 5–10% better 5y OS than N1b(2–3+); N2a(4–6+) ∼12% better 5y OS than N2b(>7+) by T category. Conclusions: This population- based outcomes analysis validates the Rectal Pooled Analysis data and supports the shift of T1–2N2 cancers from IIIC to IIIA/IIIB and T4bN1 from IIIB to IIIC. It also supports subdividing IIB into IIB(T4aN0) or IIC(T4bN0) and shifting favorable TN2 categories from IIIC to IIIA(T1N2a) or IIIB(T1N2b, T2N2a-b, T3N2a, T4aN2a). Outcomes by TN category suggest a complex biological interaction between depth of primary invasion and nodal metastases. TN Category Rectal Pooled 5y OS Pt Proposed TNM 7th Ed. SEER, Rectal 5y Observed SR Pt SEER, Colon 5y Observed SR Pt No. % No. % SE No. % SE T1–2N0 – – I 9,961 77.6 0.5% 23,861 76.3 0.3% T3N0 668 74 IIA 10,615 64.0 0.5 40,338 66.7 0.3 T4N0 95 65 IIB, T4a 818 55.7 1.9 5,020 60.6 0.8 IIC, T4b 769 44.7 2.1 3,088 45.7 1.0 T1–2N1 225 81 IIIA 2,008 72.1 1.2 3,134 71.1 1.0 T1–2N2 180 69 IIIA/IIIB* 508 56.1 2.6 499 61.5 2.6 T3N1 544 61 IIIB 5,787 52.4 0.8 17,866 54.9 0.4 T4N1 59 33 IIIB, T4a 480 48.2 2.5 2,771 47.0 1.1 IIIC, T4b 423 24.3 2.5 1,774 27.9 1.2 T3N2 663 48 IIIC 3,755 37.5 0.9 8,566 38.1 0.6 T4N2 84 38 IIIC 705 26.4 1.9 3,036 21.7 0.9 * IIIA-T1N2a; IIIB-T2N2a, T1–2N2b No significant financial relationships to disclose.