Colorectal Cancer _ ___________________________________________________________________________
to develop colorectal cancer, while those with two affected first-degree relatives are four times more likely to develop colorectal cancer [87; 88]. Abdominal Changes The abdominal examination is typically unremarkable in patients with colorectal cancer, but the presence of a palpable tumor mass is common in advanced disease. Presence of abdominal distension indicates ascites or intestinal obstruction secondary to advanced disease. Patients are unlikely to have colorectal cancer when abdominal pain is present in the absence of other gastrointestinal symptoms, but those with colorectal cancer often have abdominal pain in addition to other symptoms. Anemia Anemia is present in close to 90% of patients with right-sided colon cancer at the time of diagnosis [190]. Other Signs and Symptoms Weight loss and anorexia are more associated with advanced disease, as are palpable lymph nodes. Endoscopic Evaluation Patients with suspected colorectal cancer require a complete colon examination, and this is best performed with colonoscopy [193; 194]. Flexible sigmoidoscopy may be appropriate for low- risk patients, such as those with isolated rectal bleeding or who are younger than 50 years of age. However, positive findings with flexible sigmoidoscopy require pre- or postoperative confirmation and additional visualization of the entire colon, because roughly 5% of patients also harbor synchronous tumors [171; 195]. In the absence of intestinal obstruction contraindicating the administration of bowel preparation, colonoscopy is the first- line investigational choice because it demonstrates the highest sensitivity for colorectal cancer of any diagnostic modality, lacks the radiation exposure of CT, and enables the removal of incidental polyps and biopsy of suspicious lesions. The disadvantages of colonoscopy include a false-negative rate of 2% to 6% and accuracy that is highly operator-dependent and strongly influenced by patient adherence to proper preparatory bowel cleansing. Tumor localization is improved with administration of intraluminal ink or tattooing of the suspected cancer site [132; 195]. Diagnostic Imaging CT colonography sensitivity in colorectal cancer detection is comparable to optical colonoscopy and has been used following incomplete colonoscopy assessment. DCBE has also been used in cases of poor colonoscopy visualization of the sigmoid colon (e.g., with severe diverticular disease), usually combined with flexible sigmoidoscopy. However, the superior sensitivity and specificity of CT colonography have led to the phasing out of DCBE for these indications [193; 194].
Elderly or frail patients may have difficulties with immobility or an inability to tolerate bowel preparation, which can impede conventional colonoscopy. One alternative is colorectal imaging using plain CT scan. Plain abdominal CT scan with oral contrast (but without bowel preparation) of symptomatic patients has shown an 88% to 94% sensitivity for colon cancer detection at 12- to 30-month follow-up [196; 197]. Laboratory Tests Serum concentrations of carcinoembryonic antigen (CEA) are elevated in about 80% of patients with colorectal cancer, but CEA lacks sufficient sensitivity or specificity for use in screening or diagnosis. Instead, its greatest value comes from detecting colorectal cancer recurrence in patients who have undergone surgical resection. Patients should have baseline CEA values measured for comparison during the surveillance period to monitor for signs of recurrence [188]. Routine complete blood count, liver biochemistry, bone mineral density profile, and renal function are recommended before treatment to establish patient baseline values, to assess for hepatic and renal metastases, and to identify anemia [188]. Differential Diagnosis During the diagnostic workup, other conditions with similarity to colon or rectal cancer should be considered and ruled out. These include [114; 171]: • Irritable bowel syndrome • Crohn disease • Ulcerative colitis • Ileus • Diverticular disease • Ischemic bowel • Arteriovenous malformation • Hemorrhoids and anal fissure in suspected rectal cancer Rare gastrointestinal tumors should also be ruled out, such as: • Carcinoid/neuroendocrine tumors
• Small-intestine carcinomas • Gastrointestinal lymphoma
STAGING OF COLON AND RECTAL CANCER Accurate staging provides crucial information about the location and size of the primary tumor, and if present, the size, number, and location of metastases. Accurate initial staging influences therapy by guiding the selection of surgical intervention and choice of neoadjuvant therapy to maximize an outcome of resection with clear margins.
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