Background: The clinical value and prognostic implications of histologic response to neoadjuvant chemotherapy in gastric cancer is unknown. Methods: Tumor regression grade (TRG) was recorded in 58 gastric cancer patients identified from two institutional surgical databases. TRG 1a/b represented histologic responders (<10% viable tumor), while TRG 2/3 represented non-responders (>10% viable tumor). Results: TRG 1a/b was recorded in 10 patients (17%), while 48 patients (83%) had a TRG 2/3 response. Larger tumor size (OR 0.24; 95%CI 0.09, 0.64; P=0.004) and clinical downstaging (OR 30.0; 95%CI 3.26, 276; P=0.003) were the only factors predictive of histologic response. TRG 1a/b responders had 3-year survival of 70.0% and an estimated overall survival of>69.8 months compared to 38.2% and 22.8 months in non-responders; however, this trend was not statistically significant (P=0.535). While TRG could not predict survival (OR 2.40; 95%CI 0.46, 12.57; P=0.300), patient age (OR 1.06; 95%CI 1.00, 1.11; P=0.035), and the number of positive lymph nodes (≥7; OR 0.05; 95%CI 0.07, 0.27; P<0.001) were independent predictors of survival. Conclusions: Few gastric cancers demonstrate histologic response to neoadjuvant chemotherapy. While TRG may be a valid marker for treatment response, its predictive value and clinical application in gastric cancer remains unclear.
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