Snapshot A 68-year-old man presents to his primary care physician for fatigue. He reports a change in his bowel habits and noticed his stool is pencil thin. He also endorses an unintentional 20-pound weight loss over the course of 2 months. His father died of colon cancer when he was 65 years of age. He has never had a colonoscopy. Physical examination is notable for tenderness upon palpation in the left abdomen. Laboratory studies are notable for iron deficiency anemia. Colonoscopy is notable for a colonic mass in the descending colon. Introduction Overview describes malignancy affecting the colon or rectum most colorectal cancer arises from an adenomatous polyp may be associated with an increased CEA Epidemiology incidence incidence has decreased due to improved screening practices (e.g., colonoscopy) demographics typically seen in ≥ 60 years of age men > women risk factors hereditary syndromes Lynch syndrome (hereditary nonpolyposis colorectal cancer) familial adenomatous polyposis MYH-associated polyposis environmental factors diets high in animal fat inflammatory bowel disease ulcerative colitis Crohn disease cigarette smoking Pathogenesis chromosomal instability pathway APC/β-catenin gene mutation initiating event in adenoma formation leads to the formation of an aberrant crypt foci KRAS mutation leads to unregulating intracellular signaling resulting in adenoma formation p53 and DCC gene mutation results in tumorgenesis and invasive cancer microsatellite instability pathway mismatch repair genes abnormal methylation or mutations leads to cancer development in patients with Lynch syndrome and certain sporadic colorectal cancers Associated conditions Streptococcus gallolyticus (previously known as Streptococcus bovis) although rare, can present with this bacteremia Presentation Clinical presentation depends on the location of the colorectal cancer Symptoms/physical exam asymptomatic these patients can be found to have colorectal cancer upon routine screening change in bowel habits typically seen in cancer affecting the descending colon rectal bleeding typically seen in rectal cancers rectal or abdominal mass unexplained iron deficiency anemia secondary to gastrointestinal bleeding typically seen in cancer affecting the ascending colon malaise, unintentional weight-loss, and fatigue Imaging Colonoscopy indication to visualize the colonic mucosa and obtain a biopsy from colonic mass to establish a histologic diagnosis gold standard for evaluating for colorectal cancer screening method low-risk patients screen at 50 years of age continue performing every 10 years first-degree relative with colon cancer screen at 40 years of age or 10 years prior to the relatives age of presentation for patients who do not want to undergo colonoscopy, other screening options include fecal immunochemical test (FIT) assesses for ocult blood in the stool computed tomography colonography Differential Diverticulitis differentiating factors inflammation of the diverticula Treatment Treatment is geared towards the staging of the malignacy Surgical resection indication performed in localized disease typically given with adjuvant chemotherapy Complications Colonic obstrucition Bowel perforation Metastasis