Acinar Cell Carcinoma of the Pancreas: Understanding Your Pathology Report

By Jason Wasserman MD PhD FRCPC
June 16, 2026

Acinar cell carcinoma is a rare type of pancreatic cancer. It starts from acinar cells, the cells that make the digestive enzymes the pancreas uses to break down food. Because the tumor cells come from these enzyme-making cells, they often continue to produce pancreatic enzymes. Acinar cell carcinoma can occur at any age, including in children, but it is most common in adults around 60 years of age and is found more often in men. The tumor can develop anywhere in the pancreas and is often large by the time it is found. Although it is a serious cancer, acinar cell carcinoma tends to have a better outlook than the most common type of pancreatic cancer, ductal adenocarcinoma.

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 acinar cell carcinoma?

The exact cause of acinar cell carcinoma is not known. Unlike ductal adenocarcinoma, it is not strongly linked to smoking. One important feature of this tumor is that a notable number of patients carry inherited changes in genes that normally help repair damaged DNA, such as BRCA2. Because an inherited change in one of these genes can also affect family members and may influence treatment, genetic counseling and testing are often recommended. This is discussed further in the biomarker section below.

What are the symptoms of acinar cell carcinoma?

The symptoms are often vague and are usually related to the size of the tumor. They may include abdominal pain, a palpable lump, nausea, a feeling of fullness, and weight loss. Because the tumor cells make digestive enzymes, a small number of patients (about 10 to 15 percent) develop a distinctive condition caused by the release of large amounts of the enzyme lipase into the blood. This can cause painful red lumps under the skin (from fat breakdown), joint pain, and an elevated count of a type of white blood cell called an eosinophil. Some tumors also raise the level of a protein called alpha-fetoprotein (AFP) in the blood.

How common is this tumor?

Acinar cell carcinoma is rare, making up only about 1 to 2 percent of cancers that start in the pancreas in adults. It also occurs in children, where it is likewise uncommon. There is no known ethnic predilection.

How is the diagnosis made?

The diagnosis is made after a tissue sample is examined under the microscope by a pathologist. The sample may be obtained by a fine needle aspiration biopsy or core needle biopsy during an endoscopic ultrasound, or from the tumor after it has been removed by surgery.

Under the microscope, acinar cell carcinoma is a cellular tumor, meaning it is composed of many tumor cells packed closely together with little supporting tissue between them. The cells often grow in small, rounded clusters that resemble normal acinar cells or in solid sheets. The cells contain granular cytoplasm filled with tiny packets of digestive enzymes, and each cell usually has a single, round nucleus with one prominent central dot called a nucleolus.

Because acinar cell carcinoma can resemble other pancreatic tumors, such as neuroendocrine tumor or solid pseudopapillary neoplasms, the pathologist usually performs immunohistochemistry, a test that uses specific stains to detect proteins in tumor cells. Acinar cell carcinomas typically stain positive for pancreatic enzymes and related proteins, such as trypsin, chymotrypsin, and BCL10, confirming that the tumor is composed of acinar cells. Some tumors also contain a smaller component of neuroendocrine or duct-forming cells; when a neuroendocrine component makes up a large part of the tumor, the diagnosis may be a mixed acinar-neuroendocrine carcinoma. Once the diagnosis is confirmed, imaging tests such as CT and MRI are used to measure the tumor and check whether it has spread.

Histologic grade

Acinar cell carcinoma is not given the well, moderately, or poorly differentiated grade used for many other cancers, because a widely accepted grading system for this tumor does not exist. The diagnosis itself tells you that the tumor is a cancer. When examining the tumor, the pathologist may comment on features such as the number of dividing cells and the presence of dead tissue (necrosis), which can provide some information about how the tumor is likely to behave. For this reason, your report may not include a grade, and this is expected.

Perineural invasion

Perineural invasion means that tumor cells are found around or along a nerve. Some cancers can use nerves as a pathway to spread into nearby tissue, so this finding is linked to a higher risk of the tumor returning after surgery. If it is present, it will be described in your pathology report.

Lymphovascular invasion

Lymphovascular invasion means that tumor cells are found inside blood vessels or lymphatic vessels. These vessels can carry tumor cells to lymph nodes or to other organs, so this finding raises the risk of spread.

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 tumor cells reach them.

Negative margin — No tumor cells are seen at the cut edge. This suggests the tumor was completely removed. The pathologist may also record the distance between the tumor and the closest margin.
Positive margin — Tumor cells are seen right at the cut edge. This raises concern that some tumor may have been left behind, and it may lead the treatment team to consider further surgery or radiation therapy.

In pancreatic surgery, the margins commonly examined include the pancreatic margin (where the pancreas was cut), the common bile duct margin, the uncinate (retroperitoneal) margin behind the pancreas, and, when part of the stomach or small intestine (duodenum) is removed, the edges of those organs.

Lymph nodes

Lymph nodes are small, bean-shaped organs that are part of the immune system, and they are a common place for pancreatic cancer to spread. When the tumor is removed, nearby lymph nodes are usually removed and examined. Your pathology report may describe the number of lymph nodes examined, the number that contain cancer, and whether extranodal extension is present. Extranodal extension means that tumor cells have broken through the outer capsule of a lymph node into the surrounding tissue. The number of lymph nodes containing cancer is used to assign the nodal stage (pN), described in the staging section below.

Biomarker and molecular testing

Biomarkers are measurable changes in tumor cells, usually involving specific genes or proteins, that help the treatment team understand how a cancer behaves and which treatments may be effective. Biomarker testing is especially valuable in acinar cell carcinoma because, unlike ductal adenocarcinoma, this tumor often carries changes that can be matched to targeted treatment or immunotherapy. In particular, acinar cell carcinoma usually lacks the KRAS gene change found in almost all ductal adenocarcinomas and more often shows changes in DNA-repair genes and the BRAF gene. Most testing is done using next-generation sequencing (NGS), a method that reads many genes at once, performed on the tumor sample. Some tests, such as those for inherited gene changes, are done on a blood or saliva sample.

DNA repair genes (BRCA1, BRCA2, PALB2, ATM)

These genes help repair damaged DNA. Changes in them are common in acinar cell carcinoma and can be inherited (germline) or arise only within the tumor (somatic). They matter for three reasons: tumors with these changes often respond better to platinum-based chemotherapy; they may respond to a type of targeted drug called a PARP inhibitor; and an inherited change has implications for family members. Because inherited changes such as in BRCA2 are found in a notable share of patients with this tumor, germline testing and genetic counseling are often recommended. Your report will state whether a change was found, and may note whether it is inherited or tumor-only.

BRAF

BRAF is a gene involved in a growth pathway, and it is altered in a meaningful number of acinar cell carcinomas. Two kinds of change are seen: a specific point change called BRAF V600E, and a “fusion,” in which the BRAF gene joins with another gene. The BRAF V600E mutation may make a tumor eligible for dabrafenib and trametinib, which is approved across cancer types, and complete responses have been reported in acinar cell carcinoma. BRAF fusions are being studied as targets in clinical trials. Testing is done by NGS. Your report will state whether a BRAF change was found and, if so, what type.

Mismatch repair (MMR) and microsatellite instability (MSI)

Mismatch repair proteins help correct small errors during DNA replication. When they are lost, the tumor is described as mismatch repair deficient (dMMR) or microsatellite unstable (MSI-high). This is uncommon in acinar cell carcinoma but important, because it may make immunotherapy (such as pembrolizumab) an option and can be a sign of Lynch syndrome, an inherited condition that raises the risk of several cancers. MMR proteins are tested by immunohistochemistry, and MSI can also be measured by NGS. Your report will describe the tumor as mismatch repair proficient (pMMR) or deficient (dMMR).

Tumor mutational burden (TMB) and NTRK fusions

Tumor mutational burden measures the number of mutations in a tumor’s DNA; a high result can make a tumor eligible for immunotherapy with pembrolizumab, which is approved across cancer types for TMB-high tumors. NTRK fusions are rare gene changes that, when present, may be treated with drugs approved across cancer types, such as larotrectinib or entrectinib. Both are uncommon in acinar cell carcinoma but are worth testing for because the matching treatments can be effective regardless of where the cancer started. Both are measured by NGS.

For more general information about the tests in this section, visit our Biomarkers section.

Pathologic stage (pTNM)

The pathologic stage describes how far the cancer has grown and spread, based on the tissue removed during surgery. It uses the TNM system (8th edition of the American Joint Committee on Cancer, or AJCC), which combines the size and extension of the tumor (pT), the involvement of lymph nodes (pN), and spread to distant organs (pM). The M part is usually determined by imaging rather than by the pathologist.

Tumor stage (pT)

pT1 — The tumor is 2 cm or smaller.
pT2 — The tumor is larger than 2 cm but not larger than 4 cm.
pT3 — The tumor is larger than 4 cm.
pT4 — The tumor has grown into nearby major arteries, such as the celiac axis, superior mesenteric artery, or common hepatic artery.

Nodal stage (pN)

pNX — The lymph nodes could not be assessed, or no lymph nodes were submitted.
pN0 — No cancer was found in any lymph nodes examined.
pN1 — Cancer was found in one to three regional lymph nodes.
pN2 — Cancer was found in four or more regional lymph nodes.

What is the prognosis?

The outlook for acinar cell carcinoma is generally better than for ductal adenocarcinoma, the most common type of pancreatic cancer. The tumor is more often able to be removed with surgery and tends to respond better to chemotherapy. Across all stages, five-year survival is often in the range of 25 to 50 percent, and it is higher for tumors that are found early and completely removed. The outlook is lower when the cancer has already spread to other organs at the time of diagnosis.

The following features are linked to a higher risk of the cancer returning or spreading:

Higher tumor stage (pT3 or pT4) — Larger tumors and tumors that involve major arteries are harder to remove completely.
Involved lymph nodes (pN1 or pN2) — Cancer in more lymph nodes is linked to a higher risk of recurrence.
Spread to distant organs — Cancer found in the liver or other organs indicates more advanced disease.
Positive surgical margins — Tumor cells at the cut edge raise the risk that some cancer was left behind.
Perineural or lymphovascular invasion — Tumor growing along nerves or within vessels is associated with a higher risk of spread.

What happens after the diagnosis?

Care for acinar cell carcinoma usually involves a team that may include a surgeon, a medical oncologist, a radiation oncologist, a pathologist, and a genetic counselor. The findings in your pathology report help this team decide on the next steps.

If the tumor can be removed, surgery is the main treatment, with the goal of removing the tumor with clear margins. The type of operation depends on where the tumor is located in the pancreas. Chemotherapy is often used as well, before surgery, after surgery, or for tumors that have spread; because acinar cell carcinoma frequently carries DNA-repair gene changes, it often responds well to platinum-based chemotherapy regimens such as FOLFIRINOX. Biomarker results help the team decide whether targeted therapy (for example, for a BRAF change) or immunotherapy (for a mismatch repair-deficient or TMB-high tumor) may be an option. Because inherited DNA-repair gene changes are relatively common in this tumor, a referral for germline genetic testing and counseling is often recommended for the patient and their family.

Supportive (palliative) care focuses on managing symptoms and maintaining quality of life. It is offered alongside other treatments from the time of diagnosis and is a standard part of care, not only an end-of-life measure. After treatment, follow-up usually includes regular imaging to watch for any return of the cancer.

Questions to ask your doctor

Where in the pancreas did the cancer start, and what was the size of the tumor?
What is the pathologic stage (pT and pN) of my cancer?
How many lymph nodes were examined, and how many contained cancer?
Were the surgical margins negative or positive?
Was perineural or lymphovascular invasion seen in my tumor?
Was biomarker or molecular testing performed, and what did it show?
Does my tumor have a BRAF mutation or a DNA repair gene mutation that could guide treatment?
Should I have germline (inherited) genetic testing, and what would it mean for my family?
Is my cancer able to be removed with surgery?
What treatments are being considered based on these findings, and in what order?
What follow-up tests will I need to watch for the cancer returning?