PREOPERATIVE RADIOTHERAPY (RT) FOR RECTAL-CANCER - PREDICTIVE FACTORSOF TUMOR DOWNSTAGING AND RESIDUAL TUMOR-CELL DENSITY (RTCD) - PROGNOSTIC IMPLICATIONS

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 wit h a histologically proven adenocarcinoma (70 T2, 65 T3, 29 T4, and 3 l ocal recurrences) underwent preoperative RT. Median dose was 44 Gy (5- 73 Gy). Surgery was performed in a mean time of 5 weeks after RT. Path ologic specimens have been reviewed by the same pathologist in order t o specify the modified Astler Coller classification (MAC), and to quan tify 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 pa tients who received a dose greater than or equal to 44 Gy had respecti vely 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 down staging, 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%) showe d an intermediate RTCD (Group 2); and 43 (26%) a high RTCD (Group 3). No predictive factor of RTCD was statistically significant. In univari ate analysis, postoperative staging was a significant prognostic facto r, with corresponding 5-year overall survival rates in 0-A, B, and C s tages of 92, 67, and 26% (p < 0.01). RTCD was not a prognostic factor. However, overall and disease-free survival rates for patients with co mplete pathologic response of 83% at 2 and 5 years suggested a better outcome in this subgroup of patients. Conclusion: The favorable influe nce of higher doses of preoperative RT on pathologic stage has been ob served. Tumor differentiation, preoperative classification and time be fore surgery were the other predictive factors of tumor downstaging. H owever, there was no predictive factor of complete pathologic response . Even after preoperative RT, postoperative staging remained a prognos tic factor. (C) 1997 Elsevier Science Inc.