Pseudoinvasive Colon Cancer Mimicking Invasive Colon Cancer: A Case Report

Pseudoinvasion refers to a condition that resembles invasive cancer despite being either a non-invasive cancer or a benign disorder. We experienced a case of non-invasive colon cancer mimicking invasive colon cancer. An 82-year-old man without any surgical or endoscopic intervention to the descending colon had a descending colon polyp, which showed Japan Narrow Band Imaging Expert Team (JNET) category type 2A. However, it was large and highly elevated, had a contracted fold, and felt tense, leading to the tentative evaluation of invasive colon cancer, though lacking full endoscopic evaluation of the mass surface due to incomplete removal of mucus. Positron emission tomography (PET), however, showed no fluorodeoxyglucose uptake in the mass. We operated on the patient with a left hemicolectomy and lymph node dissection after the pathological diagnosis of well-differentiated adenocarcinoma. Postoperative pathological study showed no lymph node metastasis, non-invasive well-differentiated adenocarcinoma cells growing in a tubular fashion, and non-invasive cancer cells growing in an inverted fashion with cystic components under the non-invasive well-differentiated adenocarcinoma cells, leading to the final evaluation of pseudoinvasion. The patient recovered uneventfully, was discharged on the eighth day after surgery, and has been well for 13 months. Endoscopic specialists should take the pseudoinvasion into consideration and perform endoscopic ultrasound evaluation when noticing discrepancies among narrow band image findings, PET findings, and pathological findings of endoscopic biopsies to avoid over-treatment for non-invasive colon cancer with pseudoinvasion.