T-stage downstaging of locally advanced rectal cancer after neoadjuvant chemoradiotherapy is not associated with reduced recurrence after adjusting for tumour characteristics.

BACKGROUND AND OBJECTIVES: Prior studies examining prognostic outcomes of locally advanced rectal adenocarcinomas achieving a complete pathological response following neoadjuvant chemoradiotherapy (nCRT) did not adjust for adverse prognostic factors in multivariate analyses and account for magnetic resonance imaging tumour staging inaccuracy pre-nCRT. We aimed to clarify prognostic outcomes in mT3 rectal adenocarcinomas with ypT-downstaging post-nCRT in robust adjusted analyses. METHODS: Retrospective analysis of prospectively-collected clinical data from 528 mT3 rectal adenocarcinomas ≤12 cm from the anal verge, any N-stage, no metastases, post-nCRT following total mesorectal excision (TME). Recurrence outcomes (local and distant combined) of tumours with complete ypT-downstaging (ypT0) post-nCRT before TME compared with no ypT-downstaging (≥ypT3) were examined using multivariate Cox regression, adjusting for confounders and accounting for pre-nCRT mT3-staging inaccuracy using bootstrapping. RESULTS: Complete ypT-downstaging was achieved in of 17.6% tumours and correlated strongly with complete pathological response. Complete ypT-downstaging was not associated with reduced recurrence hazards compared with no ypT-downstaging (hazard ratio = 0.60; 95% confidence interval [CI]: 0.23-1.56; p = 0.30). Lymphovascular invasion (LVI) and ypN+ve increased recurrence hazards by 1.8-fold (95% CI: 1.10-2.79; p = 0.02) and 2.3-fold (95% CI: 1.48-3.54; p = 0.0002), respectively. CONCLUSION: Complete ypT-downstaging was not associated with reduced recurrence after adjusting for confounders and accounting for mT3-staging inaccuracy, even in the absence of adverse prognostic factors (ypN+, LVI).