Tumors of the Pancreas: Islet Cell Tumors
Islet cell tumors of the pancreas are rare tumors and approximately 2500 cases of pancreatic islet cell tumors are seen in the United States each year. These tumors are often also called pancreatic neuroendocrine tumors.
Islet cell tumors of the pancreas are different from adenocarcinoma of the pancreas. These tumors are derived from neuroendocrine cells and tend to be slow growing tumors that are treatable even after they have metastasized. Islet cell tumors can produce dramatic symptoms since up to half of these tumors may secrete hormones that produce side effects due to excessive secretion of the hormones.
What are the different types of islet cell tumors?
The following types of islet cell tumors are recognized:
The following types of functional islet cell tumors are recognized:
- Non-functioning islet cell tumors. These are the majority of the islet cell tumors of the pancreas and may account for up to 60% of all neuroendocrine tumors of the pancreas. Patients with non-functioning tumors do not have any symptoms from excessive hormone secretion by the tumor since the tumor does not release any hormones into the blood. These tumors are often diagnosed because of non-specific abdominal symptoms that lead the physician to get a CT scan of the abdomen.
- Functional islet cell tumors. These tumors produce dramatic symptoms because of excess release of various different hormones by the tumor into the blood.
Non-functioning islet cell tumors
- Insulinoma: a tumor that produces excessive amounts of insulin.
- Gastrinoma: a tumor that produces excessive amounts of gastrin.
- Glucagonoma: an extremely rare tumor that produces excessive amounts of glucagon.
- VIPoma: an extremely rare islet cell tumor the produces excessive amounts of VIP.
- Somatostatinoma: an extremely rare tumor that produces excessive amounts of somatostatin.
Non-functioning islet cell tumors are being identified more frequently because of widespread availability of CT scan imaging. These tumors have a histological appearance of islet cell tumors but do not produce any symptoms since they do not release excessive amounts of hormones in the blood.
Because these tumors are clinically silent and do not produce any hormones, they can grow silently for a long time before they are discovered. More than 50% of all non-functioning islet cell tumors are malignant (cancerous) and at the time of diagnosis the tumors are typically large and easily localized by CT scanning or MRI.
Work-up of non-functioning islet cell tumors at USC
At USC non-functioning endocrine tumors are worked up with the following studies:
Treatment for non-functioning islet cell tumors
- High resolution thin section CT scan of the pancreas and the liver: This study is used for the diagnosis of the tumor, to assess whether there are any liver metastases and also to stage whether the tumor is confined to the pancreas or whether it has grown outside of the pancreas and is invading the surrounding blood vessels. This information is important for planning of surgery for this tumor.
- Octreotide scan: This scan is obtained prior to surgery to evaluate whether the tumor is positive on the scan. If the tumor is found to be positive on the scan then this is a useful study for following the patient after the surgery to detect early recurrences.
- Measurements of pancreatic polypeptide and chromogranin: Non functioning neuroendocrine tumors do not release any hormones that cause symptoms into the blood. Elevated amounts of two hormones that do not cause any symptoms: pancreatic polypeptide and chromogranin is found in the blood of more than 90% of patients. These two hormones are measured before surgery and during follow up after the surgery for detection of early recurrences.
Surgical removal of non-functioning islet cell tumors is often curative. Our patients are therefore evaluated for surgery and all attempts are made to try and completely remove the tumor. The type of surgery depends on the location of the tumor. These tumors typically tend to be large and therefore enucleation of the tumor is usually not possible.
For tumors located in the head of the pancreas, a Whipple operation is usually indicated whereas for tumors in the tail of the pancreas a distal pancreatectomy is required. For very small tumors, organ preservation procedures such as a pancreatic head resection or a spleen preserving distal pancreatectomy may be possible options.
Our approach is to remove these tumors preferentially by laparoscopic surgery. An open procedure is usually offered to the patient if there is presence of metastases, for very large tumors (greater than 10 centimeters), if there is invasion of the major blood vessels around the pancreas by the tumor, and by patient preference. For all other patients, the laparoscopic procedure is offered as the treatment of choice.
We offer the following laparoscopic procedures for removal of non-functioning islet cell tumors:
Functioning islet cell tumors
Functional islet cell tumors often present in a dramatic fashion due to secretion of excessive amounts of hormones such as insulin, gastrin, or glucagon. These tumors tend to present at a very early stage when the tumor is tiny and is often not readily detectable.
Localization of these tumors is an important consideration since the tumors may be very small, only a few millimeters in size, when the patient presents with major symptoms related to over secretion of the hormones.
Pre-operative tests performed to detect the functioning islet cell tumors:
The following studies are offered at USC for detecting functioning islet cell tumors:
Treatment of functioning neuroendocrine tumors
- Thin section high resolution CT scanning: The dramatic advances in CT technology now provide an opportunity to detect very small islet cell tumors. At USC the latest CT technology has allowed us to detect very small tumors that a few millimeters to as small as 5 millimeters in size.
- Endoscopic Ultrasonography: For small tumors that are not seen on CT scan endoscopic ultrasonography may identify many of these tumors.
- Octreotide Scanning: The octreotide scan is useful to localize the tumor and for following patients after the surgery whose tumors were positive on octreotide scanning for detecting early recurrences.
- Portal Venous Sampling: This test is available at USC and is used only in patients who have had prior surgery where the islet cell tumor was not detected. In this study a thin needle is introduced through the liver into the portal vein and blood is sampled from the branches the portal vein at various locations for the functioning hormone in the patient. Since all pancreatic blood drain into the portal vein, blood taken selectively from different branches of the vein allows the radiologist to pinpoint the area in the pancreas where the tumor is located. This study is very expensive and invasive and is therefore not indicated in patients who are undergoing surgery for the first time for their tumor.
- Intraoperative ultrasound: This is the most sensitive test for detecting small neuroendocrine tumors in the pancreas. The pancreas is directly imaged with a small ultrasound probe during surgery to detect tiny tumors in the pancreas.
- Experience of the surgeon: Experience of the surgeon is critical to localizing and detecting the islet cell tumors at the time of the surgery. The vast majority of the tumors are detected at the time of surgery, even where preoperative studies failed to localize the tumors prior to surgery.
The different types of functioning neuroendocrine tumors require special consideration for surgery. Surgery is tailored to the type of the tumor. For further details click on the following links: