Small bowel neuroendocrine tumors (SBNETs) are an uncommon cancer. They begin in specialized neuroendocrine cells throughout the small intestine, which have characteristics of both nerve and hormone-producing cells. Unlike more common intestinal cancers, SBNETs often grow slowly, though their behavior varies. Understanding their unique features is important for specialized management.
What Small Bowel Neuroendocrine Tumors Are
Small bowel neuroendocrine tumors originate from neuroendocrine cells distributed throughout the gastrointestinal tract’s mucosal lining. These cells possess features of both nerve and hormone-producing cells. When tumors develop, they can produce excessive hormones, leading to specific symptoms; these are “functional” tumors. Many SBNETs are “non-functional,” meaning they do not produce enough hormones to cause noticeable symptoms.
SBNETs typically grow slowly compared to other cancers. Their growth can induce a fibrotic reaction in the small intestine and mesentery, potentially leading to narrowing or twisting of the bowel. Some SBNETs can display aggressive behavior, invading surrounding tissues or spreading to distant sites.
These tumors are classified as well-differentiated Neuroendocrine Tumors (NETs) or poorly differentiated Neuroendocrine Carcinomas (NECs). NETs are slower-growing, maintain more original cell characteristics, and have a more favorable outlook. NECs are aggressive and grow rapidly. This differentiation is based on how much tumor cells resemble normal neuroendocrine cells and how quickly they are dividing, influencing the disease course and treatment strategies.
Identifying Symptoms and Diagnosis
Small bowel neuroendocrine tumors often present with non-specific symptoms, making early diagnosis challenging. Symptoms include persistent abdominal pain, changes in bowel habits like diarrhea, unexplained weight loss, and fatigue. Symptoms can arise from the tumor’s physical presence or from hormone overproduction by functional tumors. Carcinoid syndrome, characterized by facial flushing, diarrhea, and sometimes wheezing or heart valve disease, can occur when hormones bypass the liver, often seen with liver metastases.
The rarity of SBNETs, combined with non-specific symptoms, contributes to diagnostic difficulty. Patients often experience symptoms attributable to other common conditions. In some cases, these tumors are discovered incidentally during imaging for unrelated reasons.
When a small bowel neuroendocrine tumor is suspected, diagnostic methods are employed. Blood and urine tests identify specific markers, such as chromogranin A or elevated serotonin levels, indicating a functional neuroendocrine tumor. Imaging techniques like CT scans and MRI provide detailed views of the abdomen to locate tumors and assess their spread. Specialized nuclear medicine scans, such as Gallium-68 DOTATATE PET/CT, are effective for detecting well-differentiated NETs by targeting specific receptors on tumor cells. Definitive diagnosis requires obtaining tissue samples through endoscopy or biopsy for microscopic examination.
Treatment Options
Treating small bowel neuroendocrine tumors requires a multidisciplinary approach, involving surgeons, oncologists, and endocrinologists. The goal for localized tumors is complete surgical removal, which can be curative if the tumor has not spread. Surgery may involve resecting the affected small bowel portion along with any involved lymph nodes. Even when complete removal is not possible, debulking surgery to reduce tumor burden can help manage symptoms and improve outcomes.
Beyond surgery, medical therapies are available, particularly for tumors that have spread or cannot be entirely removed. Somatostatin analogs (SSAs), such as octreotide or lanreotide, control hormone-related symptoms like those in carcinoid syndrome and can slow tumor growth, especially in well-differentiated NETs. These medications mimic a natural hormone, somatostatin, which inhibits the release of various other hormones.
Targeted therapies, such as everolimus and sunitinib, interfere with specific molecular pathways involved in tumor growth and blood vessel formation, offering another option for managing advanced NETs. Chemotherapy is reserved for more aggressive, poorly differentiated Neuroendocrine Carcinomas (NECs), as these tumors respond similarly to conventional high-grade cancers. For advanced, well-differentiated NETs that express somatostatin receptors, peptide receptor radionuclide therapy (PRRT) is an option; this therapy uses a radioactive substance linked to a somatostatin analog to deliver targeted radiation directly to tumor cells. Managing symptoms not directly addressed by these therapies, such as pain or nutritional deficiencies, also forms part of comprehensive care.
Outlook and Ongoing Care
The long-term outlook for individuals with small bowel neuroendocrine tumors varies depending on several factors. These include the specific tumor type (well-differentiated NET versus poorly differentiated NEC), the stage at diagnosis, its grade (how aggressive the cells appear), and treatment response. The presence of distant metastases at diagnosis, particularly to the liver, can also influence the long-term outlook.
Given the chronic nature of many SBNETs and the potential for recurrence or progression, ongoing surveillance and follow-up care are necessary. This involves regular imaging studies, such as CT or MRI scans, and blood tests to monitor tumor markers and hormone levels. These efforts help detect changes early, allowing for timely adjustments to the treatment plan. The frequency of these appointments and tests is tailored to the individual patient’s tumor characteristics and previous treatment history.
Maintaining a good quality of life is an aspect of ongoing care, which includes managing any long-term symptoms or treatment side effects. This may involve dietary adjustments, symptom-specific medications, or other supportive therapies. Connecting with patient support groups or organizations dedicated to neuroendocrine tumors can also provide support and practical information, helping individuals navigate living with this condition.