MRI tumor volume reduction rate vs tumor regression grade in the pre-operative re-staging of locally advanced rectal cancer after chemo-radiotherapy

• The study compared the tumor volume reduction rate vs tumor regression grade.
• A statistically significant correlation is found between the tumor volume reduction rate and the tumor regression grade after chemo-radiotherapy.
• When the tumor volume reduction rate is superior to 85% no residual tumor is found in the pathologic specimen, that means a complete response to chemo-radiation therapy.
• The tumor volume reduction rate is a valid parameter of treatment response that should be included in the wider spectrum of quantitative imaging biomarkers already considered in the staging and re-staging of locally advanced rectal cancer.

ObjectiveTo compare tumor volume reduction rate (TVRR) measured by MR volumetry after preoperative chemoradiotherapy (CRT) and pathological tumor regression grade (TRG) in locally advanced rectal cancer (LARC).Material and methodsIn total, 20 patients with LARC (cT3-T4) treated with CRT followed by Total Mesorectal Excision (TME) between April 2011 and April 2013 were analyzed retrospectively.Pre- and post- CRT tumor volumes (MR volumetry) were measured on 3D MR sequences. TVRR was determined using the equation TVRR (%) = (pre-CRT tumor volume—post-CRT tumor volume) × 100/pre-CRT tumor volume. The downstaging (defined as ypT0-T2) of tumor mass was evaluated and the correlation between TVRR and TRG was calculated with the method proposed by Dworak using the Spearman rank test.ResultsThe median TVRR was 77.3% (range, 26.4–99.3%); TVRR was >60% in 18 cases (90%) and in 8 of these patients (44.4 %) it was >80%. Downstaging of tumor lesions was obtained in 15 patients (75%). In 4 cases there was a complete tumor regression (TRG4) at histological examination and in the same patients there was also a TVRR > 80% measured by MR volumetry. A statistically significant correlation between TVRR and TRG (rs = 0.5466, p = 0.0126) was observed.ConclusionTVRR after preoperative CRT correlates with TRG in LARC. The MR volumetry is a prognostic factor to estimate the tumor response after preoperative CRT. TVRR data may be an useful biomarker for tailoring surgery and postoperative adjuvant chemotherapy.