The risk of nodal disease in patients with pathological complete responses after neoadjuvant chemoradiation for rectal cancer: a systematic review, meta-analysis, and meta-regression.

Background: This systematic review and meta-analysis seek to evaluate the prevalence of nodal disease in rectal cancer patients with pathological complete responses (pCR) after neoadjuvant chemoradiotherapy (ypT0N+).

Methods: This study conformed to the PRISMA guidelines. A search was performed on major databases to identify relevant articles. Meta-analyses of pooled proportions were performed on rectal cancer with pCR and ypT0N+. Meta-regression was undertaken to identify sources of heterogeneity, and the Newcastle-Ottawa Scale (NOS) was employed to assess the risk of bias.

Results: A total of 18 studies were included, totaling 7568 patients. The overall risk of bias was low, since all studies scored 6 and above out of 9 on the NOS. Preoperatively, the pooled proportions of patients with T3/T4 tumors and clinically positive nodal disease were 84.08% (95% CI 74.19 to 91.99%) and 52.14% (95% CI 35.02 to 69.00%) respectively. The prevalence of pCR in the whole pool was 18.52% (95% CI 13.31 to 24.35%; I = 93.85%; P = 0.00), and meta-regression showed a significantly negative relationship with patient age (β = - 0.03, 95% CI - 0.03 to - 0.02; P = 0.00). The pooled prevalence of ypT0N+ was 4.61% (95% CI 2.41 to 7.28%; I = 52.27%; P = 0.01), and meta-regression demonstrated a significantly positive relationship with male gender (β = 1.06, 95% CI 1.00 to 1.12; P = 0.04).

Conclusion: There is a small risk of ypN+ in patients with pCR after neoadjuvant CRT and surgery for rectal cancer. However, further research is warranted to establish these findings and to identify predictive factors for this specific group of patients.