Supplementary Material for: The vanishing colorectal tumour: lessons from an illustrative case report

Introduction Colorectal cancer is the most frequent digestive neoplasia and is usually diagnosed by colonoscopy. Treatment is contingent on staging and other factors and generally includes a combination of endoscopic or surgical resection, chemotherapy and radiotherapy. Case Presentation A 64 year-old female patient was diagnosed with an adenocarcinoma of the ascending colon following a colonoscopy performed due to anemia. After histological confirmation and staging she was submitted to a right hemicolectomy. However, the neoplasia was not present in the surgical specimen and follow up colonoscopy did not find any lesion in the remaining colon. Histopathological and endoscopic results were reappraised and the endoscopic list of the day of the index colonoscopy was reviewed with no potential error to be found. Finally, genetic concordance of the index biopsies and surgical specimen was confirmed. Discussion Spontaneous regression of neoplasia is very rare, particularly in colorectal cancer. The mechanisms of this phenomenon are not well understood and are probably multifactorial. When the possibility of spontaneous regression is being considered, a very rigorous approach must be followed as errors, such as misidentification, are more likely. In this exemplary case we describe the steps taken to reach this surprising diagnosis.