Intraductal pancreatic mucinous neoplasm (IPMN)

by Jason Wasserman MD PhD FRCPC
July 29, 2025

An intraductal papillary mucinous neoplasm (IPMN) is a type of non-invasive pancreatic tumor. It starts from the cells that line the ducts, which are small channels that carry digestive fluids from the pancreas into the intestines. These cells produce a thick, sticky substance called mucin.

IPMNs are considered precancerous because, over time, they can develop into an invasive type of pancreatic cancer. However, not all IPMNs become cancerous, and many are found incidentally during imaging tests for other conditions.

What are the symptoms of an IPMN?

Many IPMNs do not cause symptoms and are found by accident during scans for other reasons. When symptoms do occur, they may include:

• Pain in the upper abdomen or back.

• Nausea or vomiting.

• Unexplained weight loss.

• Jaundice (yellowing of the skin and eyes).

• New-onset diabetes.

• Pancreatitis (inflammation of the pancreas).

What causes IPMN?

Doctors do not know exactly what causes IPMN. However, IPMNs are more common in older adults and may be associated with certain genetic conditions like Peutz–Jeghers syndrome or familial adenomatous polyposis (FAP). In some families with a history of pancreatic cancer, individuals may be more likely to develop an IPMN.

Where in the pancreas do IPMNs start?

IPMNs develop inside the pancreatic duct system, which includes the main pancreatic duct and smaller side branches. Most IPMNs are found in the head of the pancreas, but they can occur anywhere in the duct system. In some cases, more than one area of the pancreas may be affected.

Main duct-type IPMN

This type affects the main pancreatic duct and often causes it to become enlarged. It carries a higher risk of developing high grade dysplasia or invasive cancer. Patients with this type of IPMN are usually considered for surgery.

Branch duct-type IPMN

This type involves smaller side branches of the main duct. These tumors are more likely to show low grade dysplasia and have a lower risk of cancer. Some branch duct IPMNs can be monitored over time with imaging, especially if they are small and do not show concerning features.

Mixed duct-type IPMN

This type involves both the main duct and the side branches. Like main duct IPMNs, this type has a higher risk of cancer and is typically treated with surgery.

How is this diagnosis made?

The diagnosis of an intraductal papillary mucinous neoplasm (IPMN) often begins with imaging studies such as CT scans, MRI, or endoscopic ultrasound (EUS). These tests may show a cyst or dilated duct in the pancreas that raises concern for an IPMN. In some cases, fluid or cells from the cyst can be sampled using EUS to help confirm the diagnosis.

However, a definitive diagnosis can only be made after the entire tumor is surgically removed and examined under the microscope by a pathologist. This examination allows the pathologist to confirm the diagnosis of IPMN, determine the subtype, and assess the degree of dysplasia or the presence of invasive cancer. For this reason, surgery is often recommended when imaging or biopsy results suggest a high-risk lesion.

What does an IPMN look like under the microscope?

When examined under the microscope, an IPMN is made up of tall column-shaped cells that line the inside of a duct. These cells produce mucin, which can make the ducts appear dilated or filled with thick fluid. In some cases, the cells grow in small finger-like projections called papillae. These microscopic features help confirm that the tumor is an IPMN.

What is dysplasia and why is it important?

Dysplasia is a term pathologists use to describe how abnormal the cells look under the microscope. Dysplasia is not cancer, but it is a sign that the cells have changed in a way that may lead to cancer if not treated.

Pathologists divide dysplasia in an IPMN into two levels:

• Low grade dysplasia: This means the cells look only slightly abnormal. Most IPMNs with low grade dysplasia grow slowly and have a very low risk of turning into cancer.

• High grade dysplasia: This means the cells look more abnormal and are closer to becoming cancer. IPMNs with high grade dysplasia have a higher risk of progressing to invasive cancer and are usually removed by surgery.

Knowing the level of dysplasia helps doctors decide how the IPMN should be treated and how closely the patient should be monitored in the future.

Subtypes of IPMN based on cell appearance

Pathologists also divide IPMNs into subtypes based on the appearance of the cells under the microscope. These subtypes can provide additional clues about behavior and risk.

Gastric-type IPMN

This is the most common subtype and usually involves the branch ducts. The tumor cells look similar to cells found in the stomach. Most gastric-type IPMNs show low grade dysplasia, and the risk of invasive cancer is low.

Intestinal-type IPMN

This type usually involves the main duct. The tumor cells resemble those found in the intestine and often form villous or finger-like structures. Intestinal-type IPMNs are more likely to have high grade dysplasia and may be associated with a type of invasive cancer called colloid carcinoma, which tends to have a better prognosis than typical pancreatic cancer.

Pancreatobiliary-type IPMN

This is the least common subtype and typically affects the main duct. It is more likely to show high grade dysplasia. These IPMNs are often associated with a more aggressive form of cancer that resembles conventional pancreatic ductal adenocarcinoma.

Oncocytic-type IPMN

This rare subtype is now considered a distinct tumor. The cells are large, with pink granular cytoplasm and complex growth patterns. These tumors may look alarming under the microscope, but many behave in a less aggressive way than typical pancreatic cancer.

Can an IPMN become cancer?

Yes. Although many IPMNs stay benign (non-cancerous), some can develop into an invasive type of pancreatic cancer over time.

The risk depends on several factors, including:

• The type of duct involved (main duct types are riskier).

• The type of cells (intestinal and pancreatobiliary types are riskier).

• The grade of dysplasia (high grade dysplasia carries the highest risk).

What does IPMN with associated invasive carcinoma mean?

This means that cancer has started to grow from within the IPMN. There are two types of invasive carcinoma associated with IPMN:

• Colloid carcinoma: This cancer develops from an intestinal-type IPMN and is made of tumor cells floating in pools of mucin. It usually grows more slowly and has a better prognosis.

• Tubular (ductal) adenocarcinoma: This cancer looks like typical pancreatic cancer and tends to be more aggressive. It is often seen in pancreatobiliary-type IPMNs and some gastric-type IPMNs.

If invasive carcinoma is found, it will be staged like pancreatic ductal adenocarcinoma, and treatment will depend on how far the cancer has spread.

Margins

Margins refer to the edges or borders of tissue that are cut during surgery to remove a tumour. After the surgery, a pathologist carefully examines these margins under the microscope to check if any tumor cells are present at the very edge of the removed tissue.

• A negative margin (also called a clear margin) means no tumor cells are seen at the edge. This suggests that the tumour was likely removed completely.

• A positive margin means tumor cells are seen right at the edge of the tissue. This raises concern that some tumor may have been left behind.

The margin status is important because it helps doctors decide whether additional treatment is needed. For example, if a margin is positive, further surgery may be recommended to reduce the risk of the tumor coming back.

In pancreatic surgery, several specific margins are commonly evaluated:

• Pancreatic transection margin: This is the edge of the pancreas that was cut to remove the tumour. It is often the most important margin when the tumour is located in the head or neck of the pancreas.

• Common bile duct margin: This is the edge of the bile duct that was removed with the pancreas. The bile duct carries bile from the liver to the intestine and passes through or near the head of the pancreas.

• Uncinate (retroperitoneal) margin: This is the deep tissue margin located behind the pancreas. It is close to important blood vessels and nerves and is frequently examined for tumour involvement.

• Duodenal and gastric margins: If part of the small intestine (duodenum) or stomach is removed during surgery, the cut edges of these organs are also examined.

A report may also include the distance between the tumour and the closest margin. Even if a margin is not positive, a very close margin (such as less than 1 mm) may still increase the risk of recurrence.

What is the prognosis for someone diagnosed with an IPMN?

The prognosis for an IPMN depends on whether or not invasive cancer is present:

• IPMN with low grade dysplasia: Excellent prognosis. These tumors are often curable with surgery, and the 5-year survival rate is close to 100%.

• IPMN with high grade dysplasia: Still a very good prognosis, with 5-year survival rates between 85 and 95% after complete surgical removal.

• IPMN with associated invasive carcinoma: The prognosis depends on the type and stage of the invasive cancer. Colloid carcinoma has a better outcome, while tubular carcinoma behaves more like conventional pancreatic cancer.

Even after successful surgery, some patients are at risk of developing new IPMNs in the remaining pancreas. Regular follow-up with imaging and checkups is important.

Questions to ask your doctor

• What type of IPMN do I have?

• Is there any evidence of high grade dysplasia?

• Is there any evidence of cancer?

• Was the entire IPMN removed during surgery?

• Will I need additional treatment or follow-up?

• What is the risk of recurrence or developing cancer in the future?