Tumor regression grade in gastric cancer after preoperative therapy.

Abstract

168 Background: The AJCC 8th edition updated ypStage TNM grouping for patients with gastric cancer due to the increasing use of preoperative therapy. We previously reported that nodal status after preoperative therapy (ypN) was most predictive for overall survival (OS). We intended to investigate if tumor regression grade (TRG) of the primary tumor scored by pathologists is helpful to predict survival of gastric cancer patients treated with preoperative therapy. Methods: We reviewed an institutional database to identify patients with clinically non-metastatic gastric adenocarcinoma who underwent gastrectomy after preoperative chemo- or chemoradiation therapy. Pathology reports were reviewed, and TRG was classified into following categories: 0 (complete response), 1 (few clusters of viable tumor cells, £1-2%), 2 (significant response, viable cells £ 50%), 3 (minor or no treatment response, viable cells > 50%). Associations between TRG and clinicopathological factors were examined. Univariable and multivariable Cox regressions were performed to determine associations with OS. Results: We identified 356 patients who met study criteria, including 80 (23%) patients with GEJ tumors; 56% were white and 60% were male. Preoperative chemoradiation therapy was given to 268 (75%). Fifty-six (16%) had TRG 0, 57 (16%) had TRG 1, 128 (36%) had TRG 2, and 115 (32%) had TRG 3. There were no associations between TRG and pretreatment factors. TRG 2 or 3 was associated with advanced ypT and ypN categories (both p < 0.001), ypM1 (p = 0.004), and R1 resection (0.052). Of all patients, median OS was 6.6 y, and 5-year OS was 54.1%. TRG 3 was associated with worse OS than other groups ( p = 0.015), while there was no significant OS difference among TRG 0-2 groups ( p = 0.803) in univariate analyses. On multivariable analysis, TRG was not associated with OS after adjustment for ypN status. Conclusions: In patients with gastric cancer who underwent preoperative therapy, TRG 3 was associated with advanced ypStage and R1 resection. Patients with TRG 3 had worse OS, due to associated advanced ypStage, particularly ypN+ status. Further studies are warranted to identify better definitions of treatment response and to identify the optimal modality for obtaining ypN0 status.