Cause of a colorectal polyp in the caecum

A 63-year-old woman was referred to the gastroenterology outpatient clinic for further examination of elevated tumour marker levels. Two years earlier, she underwent total mastectomy with axillary lymph node dissection for invasive micropapillary carcinoma of the right breast (pT3N3M0 Stage IIIC, according to the Eighth Edition of the Union for International Cancer Control TNM Classification of Malignant Tumours), followed by adjuvant chemotherapy, postmastectomy radiotherapy and ongoing adjuvant endocrine therapy plus a CDK4/6 inhibitor. The patient was asymptomatic without haematochezia, and physical examination results were unremarkable. Laboratory tests revealed elevated levels of carcinoembryonic antigen (5.9 ng/mL; normal range 0–5.0 ng/mL) and cancer antigen 15–3 (46.7 U/mL; normal range 0–30 U/mL). Positron emission tomography-CT and oesophagogastroduodenoscopy revealed no significant abnormalities. Colonoscopy revealed a 15 mm reddish depressed solitary lesion in the caecum ( figure 1A–D). Magnifying endoscopy with narrow-band imaging revealed tortuous, dilated, non-loop microvessels within the lesion (figure 1E). This lesion could not be classified using Kudo’s pit pattern classification with magnifying chromocolonoscopy using crystal violet staining (figure 1F).1 The endoscopic features were atypical for conventional colorectal neoplasms. Considering the possibility of neoplastic lesions, endoscopic submucosal dissection (ESD) was performed for both diagnostic and therapeutic purposes.