Comparison of apparent diffusion coefficients of resectable mid‑high rectal adenocarcinoma and distal paracancerous tissue

Paracancerous tissues actively communicate with the tumor and undergo molecular alterations associated with tumorigenesis. Apparent diffusion coefficient (ADC) can help distinguish between rectal adenocarcinoma (RA), tumor-adjacent and tumor-distant tissues. Preoperative determining optimal distal resection margin (DRM) is crucial for formulating surgical options. The present study aimed to assess ADC differences between RA and 1 cm-layer distal paracancerous tissues, providing a potential reference basis for preoperatively determining optimal DRM. A total of 110 consecutive patients with mid-high RA undergoing preoperative diffusion-weighted imaging were included. ADCs of RA and distal paracancerous tissues located ~1, 2 and 3 cm from the tumor margin (defined as D₁, D₂ and D₃, respectively) were measured using five b-value pairs (0 and 50; 0 and 100; 0 and 800; 0 and 1,000; and 0 and 1,500 sec/mm²). Differences in ADCs between RA, D₁, D₂ and D₃ were compared using the Friedman test with a post hoc Bonferroni correction. Variables that demonstrated statistical differences in multiple pairwise comparisons underwent receiver operating characteristic (ROC) analysis to assess diagnostic performance of ADCs in distinguishing between tissues. ADC at all b-value pairs demonstrated satisfactory performance in distinguishing RA from D₁, D₂ and D₃ [areas under the ROC curves (AUCs), 0.838 to 0.996)]. When the maximum b-value was ≥800 sec/mm², the ADC of D₁ was significantly lower compared with those of D₂ and D₃ (P<0.001). ADC exhibited an optimal performance in differentiating D₁ from D₂ at b-values of 0 and 800 sec/mm², and D₁ from D₃ at b-values of 0 and 1,000 sec/mm² (AUCs: 0.652 and 0.692, respectively). However, ADCs of D₂ and D₃ demonstrated no differences at all b-value pairs (all P>0.05). In conclusion, ADC may distinguish RA from D₁, D₂ and D₃, and D₁ from D₂/D₃, but cannot distinguish between D₂ and D₃.