Evaluation of the prognostic impact of pathologic response to preoperative chemotherapy using Mandard's Tumor Regression Grade (TRG) in gastric adenocarcinoma.

Background: Perioperative chemotherapy is the gold standard in gastric cancer management. The prognostic significance of pathological response has been investigated in many malignancies, using Tumor Regression Grade (TRG). Its prognostic value in gastric cancer remains poorly known.

Aims: This study aimed to assess the prognostic value of pathological response to chemotherapy, using Mandard's TRG in gastric cancer, and to identify factors predictive of response to chemotherapy.

Methods: We retrospectively identified patients with gastric adenocarcinoma from two institutional surgical databases, with preoperative chemotherapy and subsequent gastrectomy. Pathological response was centrally reviewed using Mandard's TRG.

Results: From 325 patients resected from a gastric cancer between 1997 and 2016, 109 underwent a preoperative chemotherapy. 42% were pathologic responders (TRG1-3) and 58% non-responders (TRG4-5). Five-years overall survival (OS) was 35% for non-responders, and 73% for responders (p = 0,006). Five-years disease-free survival (DFS) was 34% for non-responders and 65% for responders (p = 0,013). In multivariate analysis, pathological response was an independent prognostic factor of poor OS: HR = 2.736 (CI95% = 1.335-5.608; p = 0.006) and DFS: HR = 2.241 (CI95% = 1.130-4.446; p = 0.021).

Conclusion: TRG after preoperative chemotherapy is an important prognostic factor in patients resected for a gastric adenocarcinoma. Further studies should be performed to evaluate if adjuvant therapy should be adapted to pathological response.