582P - Predictors of Response to Preoperative Chemoradiotherapy (Crt) for Rectal Adenocarcinoma: Biopsy Specimens Obtained 1 Week After Starting Treatment are a Reliable Prognostic Factor

Abstract

ABSTRACT Aim: Preoperative CRT is the standard of care for locally advanced rectal cancer. Patients who have pathological complete response (pCR) to CRT have good outcomes with a low risk of distant metastasis. We previously reported that changes in biopsy specimens obtained 1 week after the start of CRT are a reliable predictor of histologic response. We studied the relations between survival and changes in biopsy specimens, pCR, histologic marked regression and tumor shrinkage rate as evaluated by MRI. Methods: The study group comprised 127 patients with clinical Stage II/III rectal adenocarcinoma who received CRT (40 to 45 Gy in 20-25 fractions with concurrent oral UFT or S-1) from 2006 through 2012. Surgery was performed 6 to 8 weeks after the completion of CRT. Biopsy specimens were obtained 1 week after the start of CRT and stained with hematoxylin and eosin (H-E). Patients showing moderate changes were assigned to group A, and those showing mild changes were assigned to group B. Patients with a pCR were classified as group C, and those with no pCR were classified as group D. Patients showing histologic marked regression were assigned to E group, and those without such regression were assigned to group F. Patients with a tumor shrinkage rate of 75% or higher were classified as group G, and those with a lower rate were classified as group H. Results: The proportions of patients in each group were as follows: group A, 46%; group C, 17%; group E, 43%; and group G, 52%. The 5-year recurrence-free survival rate (RFS) and the 5-year overall survival rate (OS) were respectively as follows: 79% and 92% in group A vs. 59% and 79% in group B (p = 0.019, p = 0.127); 93% and 100% in group C vs. 64% and 82% in group D (p = 0.017 and p = 0.080); 78% and 95% in group E vs. 61% and 79% in group F (p = 0.008 and p = 0.022); and 71% and 88% in G group vs. 68% and 84% in group H (p = 0.423 and p = 0.480). Moderate changes on biopsy specimens and pCR were associated with higher rates of RFS, and histologic marked regression was associated with higher rates of RFS and OS. Conclusions: Changes of H-E stained biopsy specimens 1 week after starting CRT were a prognostic factor. A pCR and marked histologic regression in resected specimens were also prognostic factors, but changes of biopsy specimens after 1 week of CRT had the important advantage of early availability. Disclosure: All authors have declared no conflicts of interest.