A TALE OF TWO CANCERS: DO LYMPH NODE RESECTIONS TRULY MEAN THE SAME IN COLON AND RECTAL CANCERS?
Amanda Arrington*, Catherine OGrady, Mohammad Khreiss, Taylor S. Riall
University of Arizona, Tucson, AZ
Introduction:
Nodal status is critical for staging and management in colorectal cancers. Guidelines now mandate a minimum of 12 lymph nodes harvested in all surgically resected colorectal cancers. These guidelines were established in the pre-neoadjuvant therapy era for colon cancer and subsequently translated over to rectal cancer as well. However, the standard of care for any >T3 rectal cancer is neoadjuvant therapy. In addition, with improved responses to chemotherapy for colon cancer, there is an increasing proportion of colon cancers receiving neoadjuvant therapy. We hypothesize that multimodality therapy with neoadjuvant therapy (NAC) decreases LN positivity rates, downstages patients and decreases overall lymph node yields (LNY).
Methods:
Stage II and III colon and rectal cancers that underwent surgery with/without NAC from 2010-2015 were identified in the NCDB database. We compared demographics and evaluated total LNY and number of positive LNs with and without NAC as well as clinical and pathological stage to evaluate rates of downstaging with NAC.
Results:
A total of 38,774 colon cancers and 21,354 rectal cancer patients were included of which 1.6% (620) and 85.7% (18,311) received NAC, respectively. Compared to no NAC, NAC patients were more likely to be treated in an academic hospital (colon 40.5% vs 25.7%, p<0.0001, rectal 35.3% vs 32.0%, p<0.0001) and more likely to have private insurance (colon 49.8% vs 33.6%, p<0.0001, rectal 52.4% vs 41.1%, p<0.0001). Of the NAC rectal cancer patients, 81.2% underwent neoadjuvant chemoradiation and these patients had the lowest LNY at 15.5 with a LN positivity rate of 49.4% in this group. NAC patients were more likely to be downstaged (preop clinical vs. pathological staging; colon 30.2% vs 5.5%, p<0.0001, rectal 52.0% vs. 16.3% p<0.0001) and have N0 pathologic disease in rectal cancer only (65.9% vs. 49.4% rectal p<0.0001). Lymph node yields in NAC groups were lower than in no NAC population (colon 19.8 vs 21.0, p<0.01, rectal 15.7 vs 20.0 p<0.0001).
Conclusion:
NAC in both colon and rectal cancers results in overall lower LN yields and lower LN positivity rates in rectal cancers. The most dramatic decrease in LNYs was seen in the rectal neoadjuvant chemoradiation group. Historically, appropriate lymph node staging guided receipt of adjuvant chemotherapy. With NAC, all patients receive chemotherapy +/- radiation with the overall result is significantly lower rates of positive nodes and lower overall LN yields. Therefore, in the setting of neoadjuvant therapy, the current minimum number of LN guidelines is not clinically relevant.
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