What tests should I get after a Small Bowel Cancer diagnosis

Tests After a Small Bowel Cancer Diagnosis

After being diagnosed with small bowel adenocarcinoma (SBA), your medical team will recommend several important tests to understand your cancer better and guide treatment decisions. Here's what you should expect:

Initial Staging & Workup Tests

According to the NCCN Guidelines for Small Bowel Adenocarcinoma, newly diagnosed patients should have:

Imaging Studies

• CT scan of chest, abdomen, and pelvis (with contrast) - This is the primary imaging test to see the extent of your tumor and check if cancer has spread to distant organs like the lungs, liver, or lymph nodes
• MRI of abdomen/pelvis - May be used if you can't have CT contrast (for example, if you have kidney problems)
• FDG-PET/CT - Generally NOT recommended as a routine test, but may be considered if CT or MRI results are unclear, especially to evaluate potential spread to the peritoneum (the lining of your abdomen)

Blood Tests

• Complete blood count (CBC) - Checks your red blood cells, white blood cells, and platelets
• Chemistry profile - Evaluates kidney and liver function
• Tumor markers: CA 19-9 and carcinoembryonic antigen (CEA) - These are proteins that can be elevated in cancer and help track your disease over time

Endoscopy (for duodenal tumors)

• EGD with endoscopic ultrasound (EUS) - If your cancer is in the duodenum (the first part of the small bowel), your doctor will use a camera to visualize the tumor and take tissue samples if needed. EUS helps determine how deep the tumor has invaded

Molecular & Genetic Testing ⭐ CRITICAL FOR TREATMENT PLANNING

This is especially important because it directly affects your treatment options:

Mismatch Repair (MMR) or Microsatellite Instability (MSI) Testing

According to NCCN Guidelines, universal MMR/MSI testing is recommended for ALL newly diagnosed SBA patients. Here's why this matters:

• What it means: This test checks if your cancer cells have defects in their DNA repair machinery
• Why it's important:
  • Patients with dMMR (deficient mismatch repair) or MSI-H (microsatellite instability-high) tumors may be candidates for immunotherapy (checkpoint inhibitor drugs like pembrolizumab, nivolumab, or dostarlimab)
  • This finding is more common in small bowel cancer than in colon cancer, making it an especially important prognostic marker
  • It can also help identify if you have Lynch syndrome (a hereditary cancer condition)

Additional Molecular Testing (for metastatic or recurrent disease)

If your cancer has spread or come back, your doctor may also test for:

• BRAF V600E mutation - Helps identify patients who may benefit from targeted therapy (dabrafenib + trametinib combination)
• HER2 amplification - Identifies patients who might respond to HER2-targeted drugs like trastuzumab deruxtecan
• POLE/POLD1 mutations - Associated with ultra-hypermutated tumors that may respond to immunotherapy
• Tumor mutational burden (TMB) - High TMB (>50 mutations per megabase) may predict immunotherapy response

Additional Screening Tests

Depending on your tumor location and medical history:

• Celiac disease screening - If your tumor is in the jejunum or ileum
• Inflammatory bowel disease (IBD) assessment - Particularly Crohn's disease, which increases SBA risk
• Lynch syndrome genetic testing - If your MMR/MSI testing shows abnormalities

Pathology Review

Your biopsy tissue will be examined for:

• Grade (how abnormal the cells look)
• Depth of invasion (how far the tumor has grown into the bowel wall)
• Lymph node involvement (how many nodes are affected)
• Margin status (whether cancer cells are at the edges of the removed tissue)
• Lymphovascular invasion (whether cancer has invaded blood or lymph vessels)

Questions to Ask Your Oncology Team

1. Which of these tests have been completed, and which are still pending?
2. What do my MMR/MSI results show, and how does this affect my treatment options?
3. Have I been tested for Lynch syndrome, and should I be?
4. What do my tumor markers (CA 19-9 and CEA) show, and will you monitor these during treatment?
5. Based on all my test results, what stage is my cancer, and what are my treatment recommendations?
6. Are there any clinical trials I might be eligible for based on my molecular testing results?

Why This Matters

These tests serve two critical purposes:

1. Staging - Determining how advanced your cancer is
2. Treatment selection - Identifying which therapies are most likely to work for YOUR specific cancer, based on its molecular characteristics

According to NCCN Guidelines, molecular testing is increasingly important because small bowel cancer has a unique genetic profile that may open doors to targeted or immunotherapy options that weren't available even a few years ago.

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