This study evaluates the ADC value of post-RT associated with Tumor regression grade (TRG) after neoadjuvant radiotherapy for locally advanced rectal cancer.
We retrospectively analyzed 88 patients with locally advanced rectal cancer between April 2010 to September 2015. Forty-four patients underwent neoadjuvant short-course radiotherapy, and the other 44 patients underwent neoadjuvant long-course chemo-radiotherapy. The ADC value of post-RT were measured by Diffusion-weighted MRI technology. The slides of surgical specimens were reviewed and classified according to Mandard TRG. We compared patients with good response (Mandard TRG1 + 2) and patients with bad response (Mandard TRG3 + 4+5). The relationship between ADC value of post-RT and TRG was analysised.
In univariate analysis, age (P = 0.006), adjuvant chemotherapy (P = 0.023), pathological type (P = 0.024), differentiation degree (P = 0.001), distance from tumor to the anal margin (P = 0.031) and TRG (P = 0.007) were significantly associated with overall survival(OS). Multivariate analysis showed that TRG (P = 0.034) were independently prognostic of OS. There was no significant difference in OS between the long-course chemo-radiotherapy group and short-course radiotherapy group (P = 0.261). The 5-year OS between TRG1 + 2 and TRG3 + 4+5 was significant (90.9% vs 67.4%, P = 0.004). Neoadjuvant radiotherapy (P = 0.000), pT (P = 0.010), gross type (P = 0.020) and the ADC value of post-RT (P = 0.002) were significantly associated with TRG. The best critical point of ADC value of post-RT was 1.71 × 10−3mm2/s by using ROC curve in predicting TRG1 + 2. The patients with low CEA level before radiotherapy had higher ADC value of post-RT (ADC≥1.71 × 10−3mm2/s), and the difference was statistically significant (P = 0.024).
There was no significant difference in OS between long-course chemo-radiotherapy and short-course radiotherapy group. TRG can predict the efficacy of neoadjuvant long-course or short-course radiotherapy in patients with locally advanced rectal cancer. The ADC value of post-RT might predict TRG after neoadjuvant radiotherapy for patients with locally advanced rectal cancer.
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All authors have declared no conflicts of interest.