Disease Description (Causes and Symptoms)
- Definition: A rectal neuroendocrine tumor (rectal carcinoid tumor) is a tumor originating from neuroendocrine cells in the rectal mucosa and is recently classified pathologically as a “neuroendocrine tumor (NET).”
- Pathophysiology: Most are well differentiated (low grade) and grow slowly, but they may metastasize to the lymph nodes, liver, and other sites depending on tumor size, invasion of the muscular layer, and degree of differentiation.
- Causes: The exact cause is unknown. A genetic predisposition has been suggested, and the tumor mainly develops around the age of 50. There is no difference by sex. Reports indicate that the incidence is higher in Asians than in Westerners (approximately twofold).
- Main symptoms: Approximately 50% are asymptomatic and are incidentally detected during colorectal cancer screening with colonoscopy. Symptoms may include rectal pain, anal bleeding, abdominal pain, and weight loss. Carcinoid syndrome (facial flushing, diarrhea, and heart failure) is rare.
Treatment Methods
- Diagnosis and staging: Colonoscopic biopsy (immunohistochemistry); endoscopic ultrasound (EUS) to assess tumor size, depth of invasion, and nearby lymph nodes; and CT/MRI and somatostatin receptor imaging (Ga-68 DOTATATE PET/CT or somatostatin receptor scintigraphy) to determine whether metastasis is present. Biochemical adjunctive tests include 24-hour urinary 5-HIAA and blood chromogranin A (CgA), among others (these may be affected by medications and gastrointestinal conditions).
- Local treatment (endoscopic/transanal)
- Tumor size ≤ 1 cm and confined to the submucosal layer: Endoscopic resection (EMR, ESD) or transanal local excision may be possible.
- Tumor size 1–2 cm: The treatment method varies by individual and institution; local excision or rectal resection is considered depending on the degree of tumor invasion, differentiation, and the patient’s condition.
- Radical surgery
- Tumor size ≥ 2 cm, invasion of the muscular layer, or lymph node metastasis: Rectal resection (such as low anterior resection) and dissection of nearby lymph nodes are recommended.
- Systemic treatment and adjuvant therapy
- Somatostatin analogues (octreotide, lanreotide): Used to control symptoms and suppress the growth of some tumors (effective in SSTR-positive tumors).
- PRRT (such as 177Lu-DOTATATE): Considered for metastatic or unresectable SSTR-positive NETs.
- Chemotherapy/targeted therapy/radiation: In general, low-grade NETs have low sensitivity to chemotherapy and radiation. For high-grade neuroendocrine carcinoma (NEC) or advanced cases with poor differentiation, standard chemotherapy (platinum/streptozocin-based regimens, etc.) or targeted therapy (e.g., everolimus) may be considered.
- Follow-up: Follow-up after resection varies according to tumor size, stage, and resection status (e.g., endoscopic follow-up for completely resected lesions ≤ 1 cm; periodic imaging and blood marker testing for high-risk groups).
- Precautions, risk of complications, and self-care
- Bleeding, infection, and changes in rectal function (defecation and sphincter function) may occur. With radical surgery, changes in bowel habits and the possible need for a colostomy should be considered.
- Chromogranin A may be elevated with PPI use, renal failure, and other conditions, so caution is needed when interpreting the results.
- Treatment selection is determined through a multidisciplinary approach by considering tumor size, invasion, imaging findings, and the patient’s preferences together.
Checklist Before an Outpatient Visit (Including Example Questions)
- Items to prepare (documents/information to bring)
- A list of all medications currently being taken, including over-the-counter medications and dietary supplements, especially whether a PPI is being used
- Previous pathology reports (biopsy results) and colonoscopy/ultrasound/CT/MRI results (bring the images if available)
- A history of previous surgery or treatment (bring surgical records if available)
- A record of symptom changes (frequency and amount of bleeding, location and severity of pain, weight changes, etc.)
- Family history (similar diseases or endocrine-related conditions)
- Useful information to give the doctor during the outpatient visit (notes)
- Date the tumor was first detected and its course
- Recent weight changes (in kg) and changes in appetite
- Changes in bowel habits (frequency, form, pain, etc.)
- Hormone-related symptoms (facial flushing, diarrhea, etc.)
- Simple checklist before the visit
- Copies of or dates of recent tests (endoscopy/imaging/blood tests)
- Confirm instructions for test preparation, such as fasting, according to the scheduled test
Examples of General Questions to Ask the Doctor
- “What are the size and depth of invasion of my lesion, and do you think complete resection is possible?”
- “What are the recommended treatment options (endoscopic resection vs. surgery), and what are their expected advantages and disadvantages?”
- “What are the common side effects of this medication (e.g., a somatostatin analogue), and how might they affect my daily life?”
- “What is the risk of recurrence and metastasis, and how often will follow-up tests be needed?”
Examples of Disease-Specific Questions
- “How many mm (or cm) is my tumor, and is it confined to the submucosal layer on endoscopic ultrasound? (To determine whether local excision is appropriate)”
- “What imaging test do you recommend to check for lymph node or liver metastasis (CT/MRI vs. Ga-68 PET/CT), and what should the follow-up interval be?”