From the Guidelines
For suspected colorectal cancer, initial evaluation should include a complete blood count, comprehensive metabolic panel, and carcinoembryonic antigen (CEA) testing, as well as colonoscopy, which is the gold standard diagnostic test, and imaging studies such as CT scan of the chest, abdomen, and pelvis with contrast, and pelvic MRI for rectal cancer. The diagnosis and treatment of colorectal cancer have been extensively outlined in the clinical guidelines by the Chinese Society of Clinical Oncology (CSCO) 1.
When it comes to staging diagnosis, especially for patients with liver metastases that cannot be confirmed by CT, non-contrast and contrast-enhanced upper abdominal MRI is recommended as a Grade I option 1. For patients with suspected rectal cancer, high-resolution pelvic MRI is the optimal imaging method for diagnosing rectal cancer with cT3 and higher stages, cN stages, mesorectal fascia, extramural vascular invasion, and anal canal structures 1.
Key points to consider in the diagnostic workup include:
- Colonoscopy as the primary diagnostic tool, unless contraindicated 1.
- CT scan of the chest, abdomen, and pelvis with contrast for staging purposes 1.
- Pelvic MRI for detailed assessment of rectal cancer 1.
- Consideration of PET-CT for equivocal findings or high-risk patients 1.
- The role of digital rectal exams in all patients with suspected rectal cancer 1.
In terms of specific imaging modalities, contrast-enhanced chest CT is recommended for diagnosis and differential diagnosis of metastatic lymph nodes, and enhanced abdominal and pelvic CT is recommended for diagnosis of ovarian metastases and peritoneal metastases 1. For patients with contraindications to venous contrast, contrast-enhanced abdominal/pelvic MRI plus non-contrast-enhanced chest CT is recommended 1.
Ultimately, the choice of diagnostic tests should be guided by the clinical presentation, potential contraindications, and the need for accurate staging to inform treatment decisions, always prioritizing morbidity, mortality, and quality of life as the primary outcomes 1.
From the Research
Labs for Suspected Colorectal Cancer
- Carcinoembryonic antigen (CEA) levels should be measured as they are elevated in colorectal cancer and can indicate advanced or metastatic disease 2
- Liver function tests (LFTs) such as alkaline phosphatase, gamma-glutamyltranspeptidase, lactic dehydrogenase, and cholinesterase can be used to detect liver metastases, but CEA is more sensitive 3, 4
Imaging Studies for Suspected Colorectal Cancer
- Direct visualization methods such as colonoscopy can be used for early diagnosis of colorectal cancer 5, 6
- Imaging examinations such as CT scans or MRI can be used to evaluate the extent and spread of metastases, especially when liver tests are abnormal 3
- Minimally invasive methods such as liquid biopsy have received attention for early diagnosis of colorectal cancer 6
Diagnostic Strategies
- A combination of stool-based, blood-based, direct visualization, and imaging examinations can be used for early diagnosis of colorectal cancer 5
- Algorithms can be proposed to guide investigation of patients with elevated CEA levels, including those with elevated CEA after CRC resection and those with de novo elevated CEA 2