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Significance Of Lymph Node Resection After Neoadjuvant Therapy In Pancreatic, Gastric And Rectal Cancers
*Amanda K Arrington, *Catherine O'Grady, *Mohammad Khreiss, Taylor S Riall
University of Arizona, TUCSON, AZ

Objectives: GI cancers are increasingly being treated neoadjuvantly prior to surgical resection. Currently, quality metrics are linked to the number of lymph nodes (LN) resected to determine treatment and prognosis and are based on initial surgical resection. We hypothesize that multimodality therapy with neoadjuvant therapy (NAC) decreases LN positivity rates, downstages patients and decreases overall lymph node yields (LNY), questioning the validity of quality metrics.
Methods: Stomach (stage II/III), pancreatic (stage I/II/III), and rectal cancers (stage II/III) diagnosed 2010-2015 surgery with/without NAC were identified in NCDB. We evaluated total LNY and positive LNs with/without NAC as well as clinical and pathological stage to evaluate rates of downstaging.
Results: 7,934 stomach, 15,908 pancreatic and 21,354 rectal cancer patients were included of which 61.1%, 21.2% and 85.7% received NAC, respectively. NAC patients were more likely to be downstaged (39.9 % vs. 11.1% gastric p<0.0001, 30.6% vs. 3.2% pancreatic p<0.0001, 52.0% vs. 16.3% rectal p<0.0001), lower LNYs (18.1 vs. 19.1 gastric p=0.239, 18.4 vs. 19.1 pancreatic p<0.0001, 15.7 vs 20.0 rectal p<0.0001) and have N0 pathologic disease (43.6% vs. 26.7% gastric p<0.0001, 51.1% vs. 30.9% pancreatic p<0.0001, 65.9% vs. 49.4% rectal p<0.0001).
Conclusion: NAC for GI cancers results in overall lower LN yields and lower LN positivity rates. With current multimodality therapy including NAC, LN yield recommendations may not be true quality metric changing outcomes or treatment strategies.

Lymph Node Evaluation of NAC and Surgical Groups. ***P<0.001 when compared to Initial Surgery
GASTRIC Neoadjuvant (n=4846)GASTRIC Initial surgery (n=3088)PANCREATIC Neoadjuvant (n=3368)PANCREATIC Initial Surgery (n=12540)RECTAL Neoadjuvant (n=18311)RECTAL Initial Surgery (n=3043)
No Radiation1670 (34.5)***1937 (62.7)1348 (40.0)***8819 (70.3)304 (1.7)***1822 (59.9)
Neoadjuvant Radiation2792 (57.6)***0 (0.0)1601 (47.5)***0 (0.0)18268 (95.4)***0 (0.0)
Clinical Stage 1838 (24.9)***5920 (47.2)
Clinical Stage 22499 (51.6)***1971 (63.8)1981 (58.8)***6361 (50.7)7836 (42.8)***1700 (55.9)
Clinical Stage 32347 (48.4)***1117 (36.2)549 (16.3)***259 (2.1)10475 (57.2)***1343 (44.1)
Pathologically Downstaged1932 (39.9)***343 (11.1)1031 (30.6)***396 (3.2)9516 (52.0)***497 (16.3)
Pathologically Upstaged1611 (33.2)1203 (39.0)1156 (34.3)6911 (55.1)3195 (17.5)788 (25.9)
Total Lymph Node Yield18.819.118.4***19.115.7***20.0
Percent LN Positive Disease56.4***73.348.9***69.134.1***50.6


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