Impact of intratumor heterogeneity on diffusion-weighted MRI as a prognostic indicator in lower rectal cancer

Background Diffusion-weighed MRI (DWI) has the potential to reveal intra-tumor pathological heterogeneity consisting of the stroma. The present study investigated the value of intra-tumor heterogeneity evaluated by DWI for predicting the survival of patients with lower rectal cancer (LRC). Methods A total of 172 LRC patients underwent radical surgery between 2009 and 2017. Patients with T1 tumors, distant metastasis, and no pre-operative MRI were excluded. Fifty-eight cases were targeted. Intra-tumor heterogeneity on DWI was quantified by an image analysis (MRI heterogeneous score of DWI: mrHSD). All enrolled cases were divided into two groups (high and low groups) according to median mrHSD. Results Median mrHSD was 0.457 (0.170–0.823), with a higher score indicating a more heterogeneous pattern on DWI. The frequency of a clinical diagnosis of lymph node metastasis and extramural vascular invasion was higher in the high group. Three-year overall survival (OS) and relapse-free survival (RFS) rates were significantly higher in the low group than in the high group (OS: 100% vs 84.6%, p = 0.012; RFS: 85.9% vs 55.6%, p = 0.027). A univariate analysis of RFS showed that the RFS rates of poorly differentiated LRC, a positive circumferential resection margin on MRI, and high mrHSD were worse (p = 0.097, 0.086, and 0.049). A multivariate analysis revealed that high mrHSD tended to be an independent factor for predicting post-operative recurrence (HR: 2.836, p = 0.060). Conclusion The quantitative evaluation of intratumor heterogeneity on DWI has potential as an imaging biomarker for predicting post-operative recurrence.