[Effect radiotherapy on postoperative staging and residual tumor cell density in rectal cancers]

To determine predictive factors and prognostic value of tumor downstaging and sterilization after preoperative radiotherapy for rectal cancer.

Between 1977 and 1994, 167 patients with a histologically proven adenocarcinoma underwent preoperative radiotherapy (median dose, 44 Gy; mean time before surgery, 5 weeks). Pathologic specimens were reviewed by the same pathologist in order to specify the modified Astler Coller classification (MAC) and to quantify residual tumor cell density (RTCD).

According to the MAC, there were nine stage 0 (5%), 10 stage A (6%), 103 stage B1-B3 (62%) and 45 stage C1-C3 (27%) tumors. Seventeen per cent and 56% of the patients who received a dose > or = 44 Gy presented with stage 0-A and stage B1-B3 tumors, respectively, compared to 4 and 69% of those who received a dose < 44 Gy (P = 0.04). Tumor differentiation and a longer interval before surgery were significantly associated with more frequent downstaging. According to the RTCD, 62 tumors (37%) showed no or only rare foci of residual tumor cells; 62 (37%) showed an intermediate RTCD and 43 (26%) a high RTCD. No predictive factor of RTCD was statistically significant. Only post-operative staging was a significant prognostic factor (P < 0.01).

The favourable influence of higher doses of preoperative radiotherapy on pathologic stage has been observed. Tumor differentiation and time before surgery were the other significant predictive factors of tumor downstaging. Even after preoperative radiotherapy, post-operative staging retained its prognostic value.