PANCE Blueprint GI and Nutrition (9%)

A biopsy of the mass during colonoscopy is the most appropriate next step for this patient. Histological examination of the biopsy specimen is crucial for confirming the diagnosis of colon cancer and determining the appropriate treatment plan.

For localized stage II colon cancer, the standard treatment is surgical resection of the tumor and associated lymph nodes, followed by adjuvant chemotherapy based on specific risk factors (e.g., poor differentiation, close or positive margins, lymphovascular invasion). This approach aims to remove the cancer and reduce the risk of recurrence.

The majority of colon carcinomas originate from adenomatous polyps through the adenoma-carcinoma sequence, a well-documented pathway in colorectal cancer development. These polyps are considered precancerous, and their transformation into cancer is influenced by various genetic and environmental factors.

Both adenomas and the subsequent evolved adenocarcinomas increase in incidence with age, and the distribution of adenomas and cancer in the bowel is similar. Overall, adenomatous polyps are found in approximately 25% of asymptomatic patients who undergo screening colonoscopy. The age-related prevalence of adenomatous polyps is 30% at age 50 years, 40% at age 60 years, 50% at age 70 years, and 55% at age 80 years.

The current U.S. Preventive Services Task Force recommends colorectal cancer screening for all people aged 45 years or older. Screening reduces mortality. Acceptable screening methods include Stool-based tests, colonoscopy, sigmoidoscopy, and CT colonography. Colonoscopy provides an alternative that will find abnormalities throughout the colon and allows removal of polyps at the same time; however, the major complication rate of 1 in 1000 procedures (under the best of circumstances) and the difficult preparation make many patients concerned about the process. Flexible sigmoidoscopy also provides a clear picture, but only of the distal third of the colon. Stool-based tests include the high-sensitivity guaiac fecal occult blood test (gFOBT), fecal immunochemical test (FIT), and stool DNA test. Both high-sensitivity gFOBT and FIT detect blood in the stool; however, they use different methods. High-sensitivity gFOBT is based on chemical detection of blood, while FIT uses antibodies to detect blood. Stool DNA tests detect DNA biomarkers for cancer in cells shed from the lining of the colon and rectum into stool.

CEA is a type of glycoprotein located on the cell membranes of various tissues, fluids, and excretions, including urine and feces, and is also present in cancerous growths of the colon and rectum. This antigen can enter the bloodstream, where it is detectable through a serum radioimmunoassay. Elevated levels of CEA are not exclusive to colorectal cancer but are also observed in other types of gastrointestinal and non-gastrointestinal cancers. About 70% of individuals with adenocarcinoma of the large intestine exhibit high CEA levels, though less than half of those with localized disease test positive for CEA. Due to issues with its sensitivity and specificity, CEA is not effective as a screening tool or for diagnosing colorectal cancer at a treatable stage. Nonetheless, high CEA levels before surgery are linked to a higher chance of cancer returning post-operation, and CEA levels that do not return to normal after tumor removal suggest a negative outlook. CEA monitoring is useful for identifying cancer recurrence following surgical removal, as initial normalization followed by a gradual increase in CEA levels during follow-up often indicates the cancer has returned. Elevated CEA is not specifically associated with colorectal cancer; abnormally high levels of CEA are also found in patients with other gastrointestinal malignant neoplasms and nongastrointestinal malignant neoplasms. CEA levels are elevated in 70% of patients with an adenocarcinoma of the large bowel, but less than 50% of patients with localized disease are CEA positive. Thus, because of these difficulties with sensitivity and specificity, CEA does not serve as a useful screening procedure, nor is it an accurate diagnostic test for colorectal cancer at a curable stage. However, elevated preoperative CEA levels correlate with postoperative recurrence rate, and failure of CEA to fall to normal levels after resection implies a poor prognosis. CEA is helpful in detecting recurrence after curative surgical resection; if high CEA levels return to normal after operation and then increase progressively during the follow-up period, recurrence of cancer is likely.