S1838 Cutting into Colorectal Cancer Prevention: Development of Lymph Node Metastasis Despite Clear Margins

Abstract

INTRODUCTION: Colorectal cancer (CRC) is the 2nd leading cause of cancer related death within the US despite progressively declining mortality. Advancements in screening guidelines and colonoscopy techniques led to higher adenoma detection rate and increased malignant polyp resection. Although complete resection of malignant polyps with clear margins prevents recurrence, patients are not guaranteed to be CRC risk free. Cancer may be found in the polypectomy site or lymph nodes (LNs). Here we present a case of a polypectomy with clear margins in the sigmoid colon and later findings of metastatic disease to the LNs. CASE DESCRIPTION/METHODS: A 45 y.o. male with a PMH of HTN presented to the outpatient gastroenterologist (GI) office with rectal bleeding for one month. He reported multiple bright red formed stools. FHx was relevant only for his father with h/o benign colon polyps. Colonoscopy 3 weeks later revealed a 50 mm pedunculated polyp in the sigmoid colon. Hot snare excisional polypectomy was performed and the area was tattooed. Histopathology revealed an intact well-differentiated adenocarcinoma invading into the stalk of the tubulovillous adenoma. Stalk margin was negative for invasive carcinoma by 3 mm and staged PT1,pNX with no lymphovascular invasion. Extra vigilance by the patient led to a colorectal surgery follow up. After evaluation, sigmoid colon resection with LN dissection was done. Although no residual adenocarcinoma was identified, 1 of 13 LNs dissected was positive of metastatic adenocarcinoma. The patient was discharged with a 3 month follow up with GI. He underwent chemoradiation and a repeat PET scan at 1 year which was negative for residual disease. Repeat colonoscopy at 1 and 3 years was negative for recurrence. DISCUSSION: Colonoscopy remains the gold standard for detecting and treating polyps. Several studies support demonstrating clear margins to show entire adenoma removal on histopathological examination. Resections >1 mm of free margins show 0–2% recurrence while <1 mm demonstrate 21–33%. Ideally, samples should have >2 mm of free margins but recurrence chances are not 0%. Therefore, individual decisions should be made for discussing possible LN metastasis which inevitably cause recurrence despite complete polyp resection.Close surveillance with oncology and colorectal surgery should be considered in large malignant polyps.Figure 1.: 50mm rectosigmoid polyp with stalk.Figure 2.: Polypectomy with 3mm cancer free margin.Figure 3.: Lymph node with metastatic adenocarcinoma.