Early regression index (ERI) on MR images as response predictor in esophageal cancer treated with neoadjuvant chemo-radiotherapy: Interim analysis of the prospective ESCAPE trial.

Purpose: The early regression index (ERI) predicts treatment response in rectal cancer patients. Aim of current study was to prospectively assess tumor response to neoadjuvant chemo-radiotherapy (nCRT) of locally advanced esophageal cancer using ERI, based on MRI.

Material And Methods: From January 2020 to May 2023, 30 patients with esophageal cancer were enrolled in a prospective study (ESCAPE). PET-MRI was performed: i) before nCRT (t); ii) at mid-radiotherapy, t; iii) after nCRT, 2-6 weeks before surgery (t); nCRT delivered 41.4 Gy/23fr with concurrent carboplatin and paclitaxel. For patients that skipped surgery, complete clinical response (cCR) was assessed if patients showed no local relapse after 18 months; patients with pathological complete response (pCR) or with cCR were considered as complete responders (pCR + cCR). GTV volumes were delineated by two observers (V, V, V) on T2w MRI: ERI and other volume regression parameters at t and t were tested as predictors of pCR + cCR.

Results: Complete data of 25 patients were available at the time of the analysis: 3/25 with complete response at imaging refused surgery and 2/3 were cCR; in total, 10/25 patients showed pCR + cCR (pCR = 8/22). Both ERI and ERI classified pCR + cCR patients, with ERI showing better performance (AUC:0.78, p = 0.014): A two-variable logistic model combining ERI and V improved performances (AUC:0.93, p < 0.0001). Inter-observer variability in contouring GTV did not affect the results.

Conclusions: Despite the limited numbers, interim analysis of ESCAPE study suggests ERI as a potential predictor of complete response after nCRT for esophageal cancer. Further validation on larger populations is warranted.