by Max Knapp MD and Jason Wasserman MD PhD FRCPC
November 2, 2023
Intraductal pancreatic mucinous neoplasm (IPMN) is a non-cancerous type of pancreatic tumour. Although this type of tumour is considered non-cancerous, it has the potential to change into a type of pancreatic cancer called adenocarcinoma over time. The risk of developing cancer is higher for tumours that arise in the main pancreatic duct and for those with high grade dysplasia (see sections below for more information).
On average, patients diagnosed with IPMN are around 60 years of age, but patients can be younger or older. The tumour is usually located in the part of the pancreas closest to the small bowel (the “head” of the pancreas), but it can arise anywhere along the length of the pancreas.
Most IPMNs do not cause any symptoms and the tumour is found incidentally when an imaging test such as a CT scan or MRI is performed for another reason. However, if an IPMN becomes large, it may cause symptoms by stopping bile flow from the liver or pressing on surrounding organs. These symptoms may include bloating, nausea, abdominal pain, or changes in the colour or consistency of stool.
Currently, we do not know what causes IPMN. However, people with certain genetic conditions such as Peutz-Jeghers syndrome, familial adenomatous polyposis, and McCune–Albright syndrome appear to be more likely to develop this type of tumour.
The diagnosis of IPMN is based on a combination of radiologic imaging and microscopic examination of the tumour by a pathologist.
IPMN is composed of one or multiple open spaces called cysts. The cysts are lined with specialized goblet cells that produce a substance called mucin. In an IPMN, these cells can look similar to cells from a variety of different organs in the digestive tract. For example, the cells may resemble normal cells from the stomach, intestines, or the bile ducts within the pancreas. If the cells resemble stomach cells, the tumor is called a gastric-type IPMN. If the cells resemble intestinal cells, the tumor is called an intestinal-type IPMN. If the cells resemble bile ducts, the tumor is called pancreatobiliary IPMN. The types of cells found in the IPMN do not change the behavior of the tumour – they are all noncancerous.
Dysplasia is an abnormal pattern of growth and maturation, and it is seen in all IPMNs. Pathologists divide dysplasia in an IPMN into two grades – low grade dysplasia and high grade dysplasia. All IPMN show at least low grade dysplasia but high grade dysplasia is important because it is associated with a greater risk of developing into a type of pancreatic cancer called adenocarcinoma. Intestinal-type and pancreatobiliary-type IPMN are commonly associated with high grade dysplasia while gastric-type IPMN are typically low grade.
Invasive carcinoma is a term used to describe a cancerous tumour that has spread into surrounding tissues. IPMNs with high grade dysplasia (also known as high grade IPMN) can turn into a type of invasive carcinoma called adenocarcinoma over time. Invasive carcinoma is more likely to develop in tumour located within the main pancreatic duct (a large channel that runs through the middle of the pancreas) compared to a tumour located in a side branch (one of the smaller channels that lead to the main duct).
The prognosis for a patient with invasive carcinoma arising from an IPMN depends on several factors. Most important is the distance the invasive tumour cells have traveled into the pancreas. For example, tumours that show less than 5 mm of invasion are associated with a very good prognosis compared to tumours with more than 5 mm of invasion. In contrast, tumours that spread beyond the pancreas into surrounding organs are associated with poor prognosis.
In pathology, a margin is the edge of a tissue that is cut when removing a tumor from the body. The margins described in a pathology report are very important because they tell you if the entire tumor was removed or if some of the tumor was left behind. The margin status will determine what (if any) additional treatment you may require.
Most pathology reports only describe margins after surgery has been performed to remove the entire tumour. For this reason, margins are not usually described after a procedure called a biopsy is performed to remove only part of the tumor. The number of margins described in a pathology report depends on the types of tissues removed and the location of the tumor. The size of the margin (the amount of normal tissue between the tumor and the cut edge) depends on the type of tumor being removed and the location of the tumor.
The two most important margins in the pancreas are:
Other margins that may be described in your report include:
Pathologists carefully examine the margins to look for tumor cells at the cut edge of the tissue. If tumor cells are seen at the cut edge of the tissue, the margin will be described as positive. If no tumor cells are seen at the cut edge of the tissue, a margin will be described as negative. Even if all of the margins are negative, some pathology reports will also provide a measurement of the closest tumor cells to the cut edge of the tissue.
A positive (or very close) margin is important because it means that tumor cells may have been left behind in your body when the tumor was surgically removed. For this reason, patients who have a positive margin may be offered another surgery to remove the rest of the tumor or radiation therapy to the area of the body with the positive margin. The decision to offer additional treatment and the type of treatment options offered will depend on a variety of factors including the type of tumor removed and the area of the body involved. For example, additional treatment may not be necessary for an IPMN with low grade dysplasia but may be strongly advised for an IPMN with high grade dysplasia or invasive carcinoma.
IPMN is believed to arise from a small noncancerous change called pancreatic intraepithelial neoplasia (PanIN). For this reason, is it not unusual for pathologists to see PanIN in the tissue surrounding an IPMN. If PanIN is seen, it will be described in your report.
This article was written by doctors to help you read and understand your pathology report for IPMN. The sections above describe the results found in most pathology reports, however, all reports are different and results may vary. Importantly, some of this information will only be described in your report after the entire tumour has been surgically removed and examined by a pathologist. Contact us if you have any questions about this article or your pathology report. Read this article for a more general introduction to the parts of a typical pathology report.