What tests do I need right after being diagnosed with Colorectal Cancer

Tests You Need Right After a Colorectal Cancer Diagnosis

When you're first diagnosed with colorectal cancer, your care team will order several important tests. These help them understand the extent of your cancer and plan your treatment. Let me walk you through what to expect.

Core Diagnostic Tests

Pathology & Molecular Testing (From Your Tumor)

Your tumor tissue will be examined in detail. According to the NCCN Guidelines for Colon Cancer, this includes:

• Mismatch Repair (MMR) or Microsatellite Instability (MSI) testing - This checks how well your body's DNA repair system works. This is universal (recommended for everyone) and is critical because it affects treatment decisions significantly.

• KRAS, NRAS, and BRAF mutation testing - These genetic tests look for specific mutations in your cancer cells. If you have certain mutations (like KRAS or NRAS), this changes which targeted therapies you can receive. The NCCN Guidelines emphasize that all patients with metastatic colorectal cancer should have this testing done, ideally as part of a comprehensive next-generation sequencing (NGS) panel.

Why this matters: These molecular tests are the "roadmap" your oncologist uses to select the most effective treatment for YOUR specific cancer.

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Imaging Tests

Chest, Abdomen, and Pelvis CT Scan (C/A/P CT)

You'll get a CT scan with contrast (a dye that makes images clearer) to see:

• If cancer has spread to your liver, lungs, or other organs
• The size and location of your tumor
• Whether nearby lymph nodes are involved

This is done before surgery or other treatment to establish your baseline.

Colonoscopy

If you haven't had a complete colonoscopy before diagnosis, your doctor will perform one to:

• Examine your entire colon
• Look for other polyps or tumors
• Take biopsies if needed

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Blood Tests

Complete Blood Count (CBC)

• Measures red blood cells, white blood cells, and platelets
• Helps assess your overall health and ability to tolerate treatment

Chemistry Panel (Metabolic Panel)

• Checks kidney and liver function
• Measures electrolytes and other important chemicals
• Important because some cancer treatments can affect these organs

CEA (Carcinoembryonic Antigen)

• A tumor marker (a protein produced by cancer cells)
• Provides a baseline to compare against during and after treatment
• According to NCCN Guidelines, if you're a potential candidate for further intervention, CEA monitoring becomes part of your surveillance plan

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Additional Considerations

Genetic/Familial Risk Assessment

According to the NCCN Guidelines, all patients with colorectal cancer should be counseled about family history. Your doctor may recommend testing for:

• Lynch syndrome (hereditary cancer syndrome)
• Familial adenomatous polyposis (FAP)

This is important because it affects screening recommendations for your family members.

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What Happens With These Results?

Your care team will use all this information to:

1. Stage your cancer (determine how advanced it is)
2. Identify treatment options (surgery, chemotherapy, targeted therapy, immunotherapy)
3. Assess prognosis (expected outcomes)
4. Plan surveillance (follow-up monitoring after treatment)

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Questions to Ask Your Oncology Team

1. "Which molecular tests have been done on my tumor, and what did they show?" - Make sure you understand your MMR/MSI status and any mutations found.

2. "What do my imaging results show about the extent of my cancer?" - Ask specifically about whether cancer has spread.

3. "Based on my test results, what treatment options are available for me?" - Different molecular findings open different treatment pathways.

4. "When will I get all my test results, and can I have copies?" - You have the right to your [ID removed] and test results.

5. "Are there any clinical trials I might be eligible for based on my cancer's characteristics?" - The NCCN Guidelines note that treating patients in clinical trials has priority over standard therapy when available.

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Important Timeline Note

These tests typically happen within 1-2 weeks of diagnosis. Some results (like pathology) may take 1-2 weeks, while imaging and blood work are usually available within days. Don't be alarmed if you're waiting for results—this is normal and allows your team to develop a comprehensive treatment plan.

This information is for educational purposes only. Always consult your healthcare team for personalized medical advice and decisions.

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Sources:

• NCCN Guidelines for Colon Cancer (Version 5.2025)
• NCCN Guidelines for Rectal Cancer (Version 4.2025)