Prognostic implications of downstaging following preoperative radiation therapy for operable T3-T4 rectal cancer

To evaluate the prognostic value of tumor downstaging after preoperative radiation for resectable rectal cancer.

Eighty-eight patients with non-metastatic resectable rectal cancers (76 T3 and 12 T4) were treated with preoperative irradiation. Median dose was 40 Gy (30-46 Gy) delivered over 32 days (range 11-40). Seventeen patients received preoperative chemotherapy, two courses of 5-fluorouracil (5FU) 350 mg/m2/day and folinic acid 20 mg/m2/day; 5 days per week during the first and fifth weeks of radiotherapy. Surgery was performed with a mean delay of 46 days after completion of irradiation and included 66 abdominoperineal resections and 22 anal sphincter-preserving procedures. Postoperative chemotherapy was administered in 44 patients.

Histological tumor stages were: complete histological response in 7%, pT2N0 in 19%, pT3N0 in 46%, and pT2-3N1 in 28%. Tumor downstaging occurred in 26%. No predictive factor of downstaging was statistically significant. The median follow-up was 33 months. The 3- and 5-year cancer-specific survival rates were 100% for the pT0N0 and pT2N0, respectively, 89% and 68% for pT3N0, and 64% and 0% for pT2T3N1. After preoperative irradiation, the pathological tumor stages remained a prognostic factor. Patients with downstaging (pT0T2N0) had significantly higher cancer-specific survival rates than the group without downstaging: 100% and 80% at 3 years, and 100% and 45% at 5 years; respectively (p = 0.011). The 3- and 5-year recurrence free-survival rates were 94% for the group with downstaging and 56% and 50%, respectively, for the group without downstaging (p = 0.002).

Downstaging after preoperative irradiation in this retrospective study results in an improvement in local control and survival.