Correlation Between MRI and Histopathology in Assessing Treatment Response to Neoadjuvant Chemoradiation in Locally Advanced Rectal Cancer

Background and Aims

Recognizing the predictive factors of response to chemoradiation is of utmost importance in patients with locally advanced rectal cancer (LARC). The study is designed to explore the correlation between post-neoadjuvant chemoradiation (nCRT) pathologic and MR-based tumor staging in LARC.

Methods

Patients with non-metastatic LARC underwent contrast-enhanced pelvic MRI before and after treatment, received standard chemoradiation, and were evaluated for tumor response. Tumor regression grade (TRG) based on histopathology ranged from TRG0 to TRG3, while MR-based responses encompassed complete response, partial response, stable disease, and progressive disease. The primary endpoints were the correlation and agreement between post-nCRT histopathologic- and MR-based tumor staging. The secondary endpoints focused on predictive factors influencing the response to nCRT and assessing the effectiveness of MRI in identifying complete pathologic response (pCR).

Results

The analysis showed a strong positive correlation (r = 0.86, p < 0.001) with moderate agreement (κ = 0.44) between post-nCRT MR- and histopathologic-based disease staging. According to multivariate analysis, initial tumor stage could predict clinical response to nCRT, and MR-based TRG could predict histopathologic response. MRI exhibited a specificity of 96.2%, sensitivity of 22.2%, positive predictive value of 50%, and negative predictive value of 88.1% in detecting pCR.

Conclusions

The study highlights the promising role of MRI in assessing treatment response in LARC, guiding clinical decision-making and potentially reducing the need for invasive procedures to evaluate treatment effectiveness.