Rectal prognostic index (RPI) to predict outcome of patients with locally advanced rectal cancer (LARC) treated with preoperative chemo-radiation (preop-CRT)
e15139 Background: Preop-CRT followed by surgical resection is the standard for LARC. LARC patients (pts) treated with preop-CRT have 60–70% 5-year survival. Several pathologic features including T stage (yT), lymph node (N) ratio (# of positive N (Np) / # of N examined (Ne)) and tumor regression grade (TRG) have been shown to be independent prognostic markers. We developed a prognostic score to determine pts with low risk of recurrence after preop-CRT. Methods: Our sample set consists of 20 pts treated on in house trial of preop-CRT with paclitaxel. All pts had R0 resections and received 4 months of 5-FU based adjuvant chemotherapy. All pathology slides were independently reviewed by GI pathologist. RPI scale of -4 to 14 was developed based on the formula: RPI = T (1–4) + (Np/Ne x 10) - TRG (0–4). The low, intermediate and high risk for recurrence were predefined as RPI (≤1), (>1 and <5), (≥5). Results: Between 1999–2003, 20 pts were treated on the trial and had R0 resection. The data is summarized in table 1 . The 5yr disease-free (DFS) and overall survival (OS) rate of all pts were 62 and 77%. Two pts (10%) achieved complete pathological response. Low, intermediate and high risk RPI was noted in 50, 35, and 15 % of pts. The 5yr DFS and OS for low, intermediate and high risk groups were 75, 42, 33 % and 86, 71 and 33% respectively.Conclusions: RPI can accurately predict a subset of pts with low risk of recurrence after preop-CRT. Majority of pts in this cohort have low risk RPI and have a favorable outcome (5yr survival rate of 86%). RPI could be very helpful in designing future trials tailoring adjuvant chemotherapy based on risk of recurrence. We are validating this data with a larger, independent group of LARC patients from our cancer registry (N=30) and this data will be available for presentation. Since RPI only requires the final pathology after CRT, it should be readily reproducible in future prospective studies across different institutions. [Table: see text] No significant financial relationships to disclose.