Colorectal intramucosal carcinoma with lymphatic invasion and lymph node metastasis: a case report

Colorectal intramucosal carcinoma (IMC) is considered to carry negligible risk of lymph node metastasis, reflecting the presumed absence of lymphatics within the lamina propria, and current guidelines endorse endoscopic resection alone as curative. We report a 64-year-old man in whom endoscopic submucosal dissection of a lower rectal tumor revealed a well-differentiated IMC with extensive lymphatic invasion confirmed by D2-40 immunostaining. Subsequent laparoscopic ultralow anterior resection showed no residual tumor at the primary site but confirmed metastasis in one of 12 regional lymph nodes. The tumor was microsatellite-stable, epidermal growth factor receptor-positive, and harbored a KRAS codon 13 mutation (G13X). The patient received adjuvant chemoradiotherapy and remained disease-free at 2 years. This case demonstrates that regional lymph node metastasis can occur in colorectal IMC even without conventional adverse histologic features such as poor differentiation or tumor budding, challenging current risk-stratification frameworks and supporting a more cautious approach when lymphatic invasion is identified.