Snapshot A 66-year-old man presents to his primary care physician for a routine exam. He reports a change in his bowel habits and noticed his stool is pencil thin. He also endorses an unintentional 15-pound weight loss over the course of 1 month. His father died of colon cancer when he was 65 years of age. Physical examination is notable for tenderness upon palpation in the left abdomen. 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 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 ETIOLOGY Pathogenesis chromosomal instability pathway APC/β-catenin gene mutation login to view 2 more bullets KRAS mutation login to view 1 more bullet p53 and DCC gene mutation login to view 1 more bullet microsatellite instability pathway mismatch repair genes login to view 1 more bullet 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 warranting colonoscopy 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 age > 50 years sudden and unprovoked deep vein thrombosis 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 login to view 9 more bullets Differential Diverticulitis differentiating factors inflammation of the diverticula Treatment Treatment is geared towards the staging of the malignacy Surgical resection indication login to view 2 more bullets