A Case of Solitary Residual Lateral Pelvic Lymph Node Metastasis Despite Complete Response of Primary Rectal Cancer Followed by Neoadjuvant Chemoradiotherapy

A 45-year-old woman was referred to our hospital complaining of diarrhea. Colonoscopy showed a rectal tumor. Histological examination showed moderately differentiated adenocarcinoma. A CT scan revealed a tumor extending from the lower rectum to the anal canal with a lateral pelvic lymph node(LPLN)swelling. We administered neoadjuvant chemoradiotherapy (45 Gy/25 Fr, S-1 80mg/m / 2/day)and the tumor and LPLN shrank remarkably, with a clinically complete response by CT and PET-CT. We then performed abdominoperineal resection with D3 lymph node and bilateral LPLN dissection. Pathological examination revealed complete disappearance of the cancer cells in the primary site, while lymph node metastasis was detected in one LPLN. We report here a rare case in which LPLN metastasis remained despite the pathological complete response of the primary tumor.