Neoadjuvant rectal score as individual-level surrogate for disease-free survival in rectal cancer in the CAO/ARO/AIO-04 randomized phase 3 trial

Abstract

BACKGROUND

Surrogate endpoints in rectal cancer after preoperative chemoradiation are lacking as their statistical validation poses major challenges, including confirmation based on large phase 3 trials. We examined the prognostic role and individual-level surrogacy of neoadjuvant rectal (NAR) score that incorporates weighted cT, ypT and ypN categories for disease-free survival (DFS) in 1191 patients with rectal carcinoma treated within the CAO/ARO/AIO-04 phase 3 trial.

PATIENTS AND METHODS

Cox regression models adjusted for treatment arm, resection status, and NAR score were used in multivariable analysis. The four Prentice criteria (PC1-4) were used to assess individual-level surrogacy of NAR for DFS.

RESULTS

After a median follow-up of 50 months, the addition of oxaliplatin to fluorouracil-based chemoradiotherapy (CRT) significantly improved 3-year DFS (75.9% [95% CI 72.30-79.50] vs 71.3% [95% CI 67.60-74.90]; P = 0.034; PC 1) and resulted in a shift towards lower NAR groups (P = 0.034, PC 2) compared to fluorouracil-only CRT. The 3-year DFS was 91.7% (95% CI, 88.2 95.2), 81.8% (95% CI, 78.4-85.1) and 58.1 (95% CI 52.4-63.9) for low, intermediate and high NAR score, respectively (P < 0.001; PC 3). NAR score remained an independent prognostic factor for DFS (low vs high NAR: HR 4.670; 95% CI 3.106-7.020; P < 0.001; low vs intermediate NAR: HR 1.971; 95% CI 1.303-2.98; P = 0.001) in multivariable analysis. Notwithstanding the inherent methodological difficulty in interpretation of PC 4 to establish surrogacy, the treatment effect on DFS was captured by NAR, supporting satisfaction of individual-level PC4.

CONCLUSION

Our study validates the prognostic role and individual-level surrogacy of NAR score for DFS within a large randomized phase 3 trial. NAR score could help oncologists to speed up response-adapted therapeutic decision, and further large phase 3 trial datasets should aim to confirm trial-level surrogacy.