Preoperative radiotherapy (RT) for rectal cancer: predictive factors of tumor downstaging and residual tumor cell density (RTCD): prognostic implications.

ABSTRACT

PURPOSE: To determine predictive factors and prognostic value of tumor downstaging and tumor sterilization after preoperative RT for rectal cancer. METHODS AND MATERIALS Between 1977 and 1994, 167 patients with a histologically proven adenocarcinoma (70 T2, 65 T3, 29 T4, and 3 local recurrences) underwent preoperative RT. Median dose was 44 Gy (5-73 Gy). Surgery was performed in a mean time of 5 weeks after RT. Pathologic specimens have been reviewed by the same pathologist in order to specify the modified Astler Coller classification (MAC), and to quantify the residual tumor cell density (RTCD). RESULTS: According to the MAC, there was 9 stage 0 (5%), 10 stage A (6%), 103 stage B1-B3 (62%), and 45 stage C1-C3 (27%) tumors. Seventeen percent and 56% of the patients who received a dose > or = 44 Gy had respectively a 0-A and a B tumor, compared to 4 and 69% in those who received a dose < 44 Gy (p = 0.04). Tumor differentiation and a longer interval before surgery were significantly associated with a more frequent downstaging, and preoperative staging correlated well to the postoperative pathological findings. According to the RTCD, 62 tumors (37%) showed no or only rare foci of residual tumor cells (Group 1); 62 (37%) showed an intermediate RTCD (Group 2); and 43 (26%) a high RTCD (Group 3). No predictive factor of RTCD was statistically significant. In univariate analysis, postoperative staging was a significant prognostic factor, with corresponding 5-year overall survival rates in 0-A, B, and C stages of 92, 67, and 26% (p < 0.01). RTCD was not a prognostic factor. However, overall and disease-free survival rates for patients with complete pathologic response of 83% at 2 and 5 years suggested a better outcome in this subgroup of patients. CONCLUSION: The favorable influence of higher doses of preoperative RT on pathologic stage has been observed. Tumor differentiation, preoperative classification and time before surgery were the other predictive factors of tumor downstaging. However, there was no predictive factor of complete pathologic response. Even after preoperative RT, postoperative staging remained a prognostic factor.