A comparative study of volumetric analysis, histopathologic downstaging, and tumor regression grade in evaluating tumor response in locally advanced rectal cancer following preoperative chemoradiation

Purpose: To compare tumor volume reduction rate, histopathologic downstaging, and tumor regression grade (TRG) among tumor responses in rectal cancer after preoperative chemoradiotherapy (CRT). Patients and Methods: Between 2002 and 2004, 30 patients with locally advanced rectal cancer underwent preoperative CRT, followed by surgical resection. Magnetic resonance volumetry was performed before and after CRT. Histopathologic tumor staging and tumor regression were reviewed. We compared pre- and post-CRT tumor volume and percent of volume reduction, according to histopathologic downstaging and TRG. Results: The tumor volume reduction rates ranged from 14.6% to 100%. Mean pre- and post-CRT tumor volumes were significantly smaller in patients who showed T downstaging than in those who did not (p = 0.040, 0.014). The mean tumor volume reduction was 66.4% vs. 55.2% (p = 0.361). However, the mean pre- and post-CRT tumor volume and mean tumor volume reduction rate between patients who showed N downstaging and those who did not were not statistically different (p = 0.176, 0.767, and 0.899). With respect to TRG, the mean pre- and post-CRT tumor volumes were not statistically significant (p = 0.108, 0.708, and 0.120). Conclusion: Tumor volume reduction rate does not correlate with histopathologic downstaging and TRG. It might be hazardous to evaluate tumor response with respect to volume reduction and to select the surgical method on this basis.