Tumor Regression Grade in Gastric Cancer After Preoperative Therapy.

BACKGROUND: The Cancer Staging Manual, 8th edition, now includes post-neoadjuvant therapy (ypTNM) staging for gastric cancer patients. Our purpose was to determine whether the tumor regression grade (TRG) of the primary tumor is useful for predicting the survival of these patients.
METHODS: We performed a retrospective review of an institutional database and identified patients with clinically non-metastatic gastric adenocarcinoma who underwent preoperative chemotherapy or chemoradiation therapy before gastrectomy. Pathology reports were reviewed, and TRG was classified as follows: 0 (complete response), 1 (viable tumor cells ≤ 1-2%), 2 (viable cells ≤ 50%), or 3 (viable cells > 50%).
RESULTS: Of the 356 patients identified, including 80 (23%) with a gastroesophageal junction tumor, 268 (75%) had undergone preoperative chemoradiation therapy. Fifty-six (16%) had TRG 0, 57 (16%) TRG 1, 128 (36%) TRG 2, and 115 (32%) TRG 3. No association between TRG and pretreatment factors was identified, except for signet-ring cell histologic type and tumor location. A higher TRG was associated with more advanced ypT and ypN categories (both p < 0.001), ypM1 (p = 0.004), and R1 resection (p = 0.052). The median overall survival (OS) duration was 6.6 years, and the 5-year OS rate was 54.1%. TRG 3 was associated with a shorter OS duration than were other TRG scores (p = 0.015), while the OS did not differ significantly among the TRG 0-2 groups (p = 0.803). On multivariable analysis, TRG was not associated with OS after adjustment for ypN status.
CONCLUSION: In gastric cancer patients who underwent preoperative therapy, TRG 3 was associated with advanced ypStage and R1 resection. Patients with TRG 3 had a shorter OS duration because of associated advanced ypStage, particularly ypN+ status.