Résumé
Colorectal cancer is rare in teenagers, especially without known risk factors. Colon cancer in young age is more likely to be diagnosed at advanced-stage, to present unfavorable tumor histology such as mucinous carcinoma, and poor outcome. We report a case of sporadic mucinous adenocarcinoma of the colon in a 19-year-old male patient without any risk factors. He complained of severe left abdominal pain that developed 1 month ago. He had a distended abdomen with severe tenderness on the left lower quadrant. A distal descending colon mass causing mechanical obstruction was observed on abdominal computed tomography. Emergency colonoscopy showed a large, fungating mass obstructing the lumen at 40 cm from the anal verge. Biopsy of the colonic mass suggested a mucinous adenocarcinoma. After decompression by colonic stent, the patient was transferred to the general surgery department for left hemicolectomy. The lesion was confirmed to be a mucinous adenocarcinoma (7.0x4.5 cm). For hereditary nonpolyposis colorectal cancer evaluation, immunohistochemical staining for MLH1 and MSH2 was normal. Reverse transcription polymerase chain reaction analysis did not detect microinstability in any of the markers tested. The patient had no familial history of cancer. Mucinous adenocarcinoma has high frequencies of poor differentiation, advanced tumor stage, loss of mismatch repair gene expression, and increased MUC2 expression. A mucinous histology is considerably more frequent in children and adolescent than in adults. Adequate invasive study is also necessary for young age patients.