Intraductal Papillary Mucinous Neoplasm (IPMN): Understanding Your Pathology Report

by Jason Wasserman MD PhD FRCPC
June 15, 2026

An intraductal papillary mucinous neoplasm (IPMN) is a type of non-invasive pancreatic tumor. It starts from the cells that line the ducts, the small channels that carry digestive fluids from the pancreas into the intestine. These cells produce a thick, sticky substance called mucin. An IPMN is not cancer, but it is considered precancerous, which means that over time, it can develop into an invasive type of pancreatic cancer. Many IPMNs never become cancerous, and many are found by chance during imaging done for other reasons.

This article will help you understand the findings in your pathology report, what each term means, and why it matters for your care.

What causes an IPMN?

Doctors do not know exactly what causes an IPMN. They are more common in older adults. In some cases, an IPMN is linked to an inherited condition such as Peutz-Jeghers syndrome or familial adenomatous polyposis (FAP), and people from families with a history of pancreatic cancer may be more likely to develop one. If an inherited condition is suspected, your doctor may suggest genetic counseling, which can also help relatives understand their own risk.

What are the symptoms of an IPMN?

Many IPMNs do not cause symptoms and are found by chance during scans done 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).

Types of IPMN based on which ducts are involved

IPMNs develop inside the pancreatic duct system, which includes the main pancreatic duct and the smaller side branches. Most are found in the head of the pancreas, but they can occur anywhere in the duct system, and sometimes more than one area is affected. Which ducts are involved is one of the most important factors in understanding the risk that an IPMN will progress to cancer.

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, and patients with this type are usually considered for surgery.

Branch duct-type IPMN

This type involves the 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, it carries a higher risk of cancer and is usually treated with surgery.

How is the diagnosis made?

The workup for an IPMN usually begins with imaging studies such as CT, MRI, or endoscopic ultrasound (EUS). These tests may show a cyst or a dilated duct in the pancreas, raising concern for an IPMN. During an EUS, fluid or cells from the cyst can sometimes be sampled with a thin needle. This fluid can be tested for certain proteins and for changes in genes such as KRAS and GNAS; a GNAS change, in particular, supports a diagnosis of IPMN and helps distinguish it from other pancreatic cysts.

A definitive diagnosis can usually be made only after the tumor is surgically removed and examined under the microscope by a pathologist. Under the microscope, an IPMN is composed of tall, column-shaped cells that line the inside of a duct and produce mucin, which can make the ducts appear dilated or filled with thick fluid. In some areas, the cells grow in small finger-like projections called papillae. Examining the whole tumor allows the pathologist to confirm the diagnosis, determine the subtype, measure the degree of dysplasia, and check for any invasive cancer. For this reason, surgery is often recommended when imaging or sampling suggests a higher-risk lesion.

Grade (degree of dysplasia)

Dysplasia describes 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 over time. Pathologists divide the dysplasia in an IPMN into two levels:

Low grade dysplasia — 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 — The cells look more abnormal and are closer to becoming cancer. IPMNs with high grade dysplasia carry a higher risk of progressing to invasive cancer and are usually removed by surgery.

Knowing the level of dysplasia helps the treatment team decide how to manage the IPMN and how closely to monitor it.

Subtypes of IPMN based on cell appearance

Pathologists also divide IPMNs into subtypes based on how the cells look under the microscope. These subtypes give additional clues about behavior and risk.

Gastric-type IPMN

This is the most common subtype and usually involves the branch ducts. The cells look similar to those 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 cells resemble those found in the intestine and often form villous or finger-like structures. Intestinal-type IPMNs are more likely to show high grade dysplasia and may be associated with a type of invasive cancer called colloid carcinoma, which tends to have a better outlook than typical pancreatic cancer.

Pancreatobiliary-type IPMN

This is a less common subtype that typically affects the main duct and is more likely to show high grade dysplasia. It is often associated with an invasive cancer that resembles conventional pancreatic ductal adenocarcinoma and tends to grow and spread more quickly.

A fourth pattern, once called oncocytic-type IPMN, is now considered a separate tumor, the intraductal oncocytic papillary neoplasm (IOPN). Its cells are large with pink, granular cytoplasm and form complex growth patterns. These tumors can look striking under the microscope, but many behave less quickly 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:

The type of duct involved (main duct types carry more risk).
The type of cells (intestinal and pancreatobiliary types carry more risk).
The grade of dysplasia (high grade dysplasia carries the highest risk).

What does “IPMN with associated invasive carcinoma” mean?

This means that cancer has begun to grow from within the IPMN. There are two main types of invasive carcinoma that can arise from an IPMN:

Colloid carcinoma — 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 outlook.
Tubular (ductal) adenocarcinoma — Looks like typical pancreatic cancer and tends to grow and spread more quickly. It is often seen with pancreatobiliary-type and some gastric-type IPMNs.

If invasive carcinoma is found, it is staged like pancreatic ductal adenocarcinoma, and the next steps depend on the type and extent of the cancer.

Surgical margins

A margin is the edge of the tissue that is cut during surgery to remove the tumor. The pathologist examines these edges under the microscope to see whether any IPMN cells reach them.

Negative margin — No IPMN cells are seen at the cut edge. This suggests the tumor was completely removed. The pathologist may also record the distance between the IPMN and the closest margin.
Positive margin — IPMN cells are seen right at the cut edge. This raises the chance that some IPMN was left behind, which can increase the risk of recurrence and may lead the treatment team to consider further surgery or closer follow-up.

In pancreatic surgery, the margins commonly examined include the pancreatic transection margin (where the pancreas was cut), the common bile duct margin, the uncinate (retroperitoneal) margin behind the pancreas, and, depending on the operation, the edges of the duodenum (small intestine) and stomach.

What is the prognosis?

The outlook for an IPMN depends mostly on whether invasive cancer is present:

IPMN with low grade dysplasia — Excellent outlook. These tumors are often cured by surgery, and five-year survival is close to 100 percent.
IPMN with high grade dysplasia — Still a very good outlook, with five-year survival in the range of 85 to 95 percent after complete surgical removal.
IPMN with associated invasive carcinoma — The outlook depends on the type and stage of the invasive cancer. Colloid carcinoma tends to have a better outcome, while tubular carcinoma behaves more like conventional pancreatic cancer.

Even after successful surgery, some patients can develop a new IPMN in the remaining pancreas, so regular follow-up with imaging remains important.

What happens after the diagnosis?

What happens next depends on the findings in your report and on your imaging. The main decision is between removing the IPMN with surgery and watching it over time with regular imaging. The treatment team weighs factors such as which ducts are involved (main duct involvement raises the concern), the grade of dysplasia, the size of the lesion, and other features on imaging such as a thickened wall or a solid nodule. Small branch duct IPMNs with low grade dysplasia and no concerning features are often monitored rather than removed, while main duct and mixed duct IPMNs, and any IPMN with high grade dysplasia, are usually treated with surgery.

When a non-invasive IPMN is completely removed, no further cancer treatment is usually needed, and care focuses on monitoring the rest of the pancreas. If invasive cancer is found, it is managed like pancreatic ductal adenocarcinoma, which may involve chemotherapy and other treatments. Care often involves a team that may include a gastroenterologist, a surgeon, a radiologist, a pathologist, and, when an inherited condition is suspected, a genetic counselor.

Questions to ask your doctor

What type of IPMN do I have (main duct, branch duct, or mixed)?
What cell subtype was found, and what does it mean for my risk?
Was there low grade or high grade dysplasia?
Is there any evidence of invasive cancer?
Was the entire IPMN removed, and were the margins negative?
Should my IPMN be removed surgically, or can it be monitored with imaging?
Will I need any additional treatment?
What is my risk of developing cancer or a new IPMN in the future?
How often should I have follow-up imaging?
Should I consider genetic counseling for myself or my family?