Significance of Lymph Node Resection after Neoadjuvant Therapy in Pancreatic, Gastric, and Rectal Cancers

Objective:Gastrointestinal cancers are increasingly being treated with NAT before surgical resection. Currently, quality metrics are linked to the number of LNs resected to determine subsequent treatment and prognosis. We hypothesize that NAT decreases LN metastasis, downstages patients, and decreases overall lymph node yields (LNY) compared to initial surgical resection. With increasing use of NAT, this brings into question the validity of quality metrics.Methods:Gastric (stage II/III), pancreatic (stage I/II/III), and rectal cancers (stage II/III) (2010-2015) treated with surgery with/without NAT were identified in National Cancer Database. We evaluated total LNY and LN metastasis with/without NAT and clinical and pathological stage to evaluate rates of downstaging.Results::A total of 7934 gastric, 15,908 pancreatic, and 21,354 rectal cancer patients were included of which 61.1%, 21.2%, and 85.7% received NAT, respectively. NAT patients were more likely to be downstaged (39.9% vs 11.1% gastric P< 0.001, 30.6% vs 3.2% pancreatic P< 0.001, 52.0% vs 16.3% rectal P< 0.001), have lower LNYs (18.8 vs 19.1 gastric P = 0.239, 18.4 vs 17.5 pancreatic P< 0.001, 15.7 vs 20.0 rectal P< 0.001) and have N0 pathologic disease (43.6% vs 26.7% gastric P< 0.001, 51.1% vs 30.9% pancreatic P< 0.001, 65.9% vs 49.4% rectal P< 0.001) when compared to initial surgical resection.Conclusion:NAT for gastrointestinal cancers results in overall lower LN yields, lower LN metastases, and significant downstaging of tumors. As all patients undergoing NAT receive multimodality therapy, LN yield recommendations may not be true quality metric changing.