Solid pseudopapillary neoplasm is a rare, slow-growing type of cancer of the pancreas. It most often affects adolescent girls and young women, although it can occur at any age and, less commonly, in men.
Despite being a cancer, this tumour usually grows slowly and responds very well to surgery. Most people do very well after treatment, especially when the tumour is completely removed.
This tumour has also been called a solid-pseudopapillary tumour or Frantz tumour.
Where does this tumour develop?
Solid pseudopapillary neoplasms arise in the pancreas, with a slight preference for the tail of the pancreas. In rare cases, very similar tumours have been reported outside the pancreas, such as in tissue behind the pancreas or, exceptionally, in the ovary or testis.
What symptoms can a solid pseudopapillary neoplasm cause?
Many people have no symptoms, and the tumour is often found incidentally during imaging done for another reason.
When symptoms occur, they are usually related to the size of the tumour. Common symptoms include abdominal discomfort, abdominal pain, or a feeling of fullness. Because these tumours can be large, abdominal injury may cause bleeding within the tumour, leading to sudden pain.
These tumours do not produce hormones, and routine blood tumour markers are usually normal.
How common is this tumour?
Solid pseudopapillary neoplasms are rare, accounting for less than 3% of pancreatic tumours overall. However, they represent a relatively large proportion of pancreatic tumours in people under 40 years of age. There is no known ethnic predilection.
What causes a solid pseudopapillary neoplasm?
The exact cause is not fully understood. The strong tendency to occur in young women suggests that hormonal factors may play a role, although the tumour itself does not cause hormone-related symptoms.
Almost all solid pseudopapillary neoplasms harbor an acquired genetic change in the CTNNB1 gene. A genetic change (mutation) is an alteration in DNA, the instruction manual inside cells. This mutation affects a protein called β-catenin, which normally helps cells stick together and controls growth signals.
In this tumour, abnormal β-catenin accumulates in the cell nucleus and activates growth-related genes. Even so, most of these tumours grow slowly, which helps explain their generally favourable behaviour.
How is the diagnosis made?
The diagnosis is made using a combination of imaging studies and examination of tumour tissue under the microscope.
Imaging
Ultrasound, CT, or MRI typically shows a well-defined mass with solid and cystic areas. Calcifications may be present. These imaging features often strongly suggest the diagnosis before surgery.
Microscopic (pathologic) features
When examined under the microscope, solid pseudopapillary neoplasms show a distinctive appearance that helps pathologists make the diagnosis and explains how this tumour behaves. Unlike normal pancreatic tissue, which is made up of specialized cells that form ducts, enzyme-producing glands, or hormone-producing clusters, the tumour cells in this condition do not resemble normal pancreatic cells. Instead, they grow abnormally and do not stick tightly to one another, a feature called poor cohesion.
The tumour typically consists of solid areas and structures called pseudopapillae. The pseudopapillary structures form when tumour cells fall away from delicate blood-vessel cores, leaving behind finger-like projections. This combination of solid growth and pseudopapillary architecture is characteristic of this tumour and gives it its name.
Additional microscopic features are common and help confirm the diagnosis. These include areas of bleeding, cyst-like spaces, cholesterol crystals, foamy immune cells, and calcifications. The tumour cells often contain small pink globules within their cytoplasm, which are helpful clues for pathologists. The cells themselves are usually uniform, with round or oval nuclei that frequently show grooves or indentations. Mitoses, which are cells in the process of dividing, are generally uncommon.
Most tumours are well defined, meaning they have clear borders separating them from the surrounding pancreas. However, small areas where tumour cells extend into nearby pancreatic tissue may be seen. Invasion into blood vessels or nerves is uncommon, which helps explain why this tumour usually behaves less aggressively than other pancreatic cancers.
In rare cases, parts of the tumour can change into a more aggressive form, a process called high-grade transformation. This means that a portion of the tumour develops features of a high-grade carcinoma. Under the microscope, these areas show sheets of more abnormal-appearing cells, larger and darker nuclei, and a higher number of dividing cells. The typical pseudopapillary pattern is often lost. High-grade transformation likely occurs when additional genetic changes build up over time, allowing a previously slow-growing tumour to behave more aggressively. Tumours with high-grade carcinoma are much more likely to spread and have a worse prognosis.
Immunohistochemistry
Immunohistochemistry uses special stains to detect proteins in tumour cells and helps confirm the diagnosis.
Solid pseudopapillary neoplasms show abnormal nuclear and cytoplasmic staining for β-catenin, which is a key diagnostic feature. Tumour cells often also express cyclin D1, vimentin, progesterone receptor, CD10, and α1-antitrypsin.
They are usually negative for chromogranin A and pancreatic enzyme markers such as trypsin. This helps distinguish them from pancreatic neuroendocrine tumours and acinar cell carcinoma.
Are molecular tests needed?
Molecular testing is usually not required. When performed, almost all tumours show a mutation in exon 3 of the CTNNB1 gene, which supports the diagnosis.
What does perineural invasion mean?
Perineural invasion (PNI) means that tumour cells are found around or along a nerve. Nerves act like small pathways through tissues, and some types of cancer can use these pathways to spread locally.
In solid pseudopapillary neoplasms, perineural invasion is uncommon. When it is present, it may suggest that the tumour is behaving in a more aggressive way, but by itself, it does not necessarily mean the cancer will spread to distant organs. Pathologists report perineural invasion because it provides information about how the tumour is interacting with nearby tissues.
What does lymphovascular invasion mean?
Lymphovascular invasion (LVI) means that tumour cells are found inside small blood vessels or lymphatic channels. These vessels are part of the body’s circulation system and can provide a route for tumour cells to spread.
Lymphovascular invasion is rare in solid pseudopapillary neoplasms. If it is identified, it suggests a higher risk of spread compared with tumours without lymphovascular invasion. Because of this, its presence or absence is an important part of the pathology report.
What are margins and why are they important?
Margins describe the edges of the tissue removed during surgery. After the tumour is removed, a pathologist examines the margins to see whether any tumour cells are present at the cut edges.
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A negative margin means no tumour cells are seen at the edge of the specimen. This suggests the tumour was removed entirely.
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A positive margin means tumour cells are present at the edge of the tissue. This suggests that some tumour may remain in the body.
In solid pseudopapillary neoplasms, complete surgical removal with negative margins is usually associated with an excellent outcome. Margin status helps guide decisions about follow-up and whether additional treatment or closer monitoring is needed.
Pathologic stage for solid pseudopapillary neoplasm
The pathologic stage for solid pseudopapillary neoplasm of the pancreas is determined using the TNM system, which stands for Tumour (T), Nodes (N), and Metastases (M). Each category is assigned a number:
Tumour stage (pT):
- T1: Tumour is 2 cm or smaller.
- T2: Tumour is larger than 2 cm but not larger than 4 cm.
- T3: Tumour is larger than 4 cm.
- T4: Tumour has spread into major nearby blood vessels.
Nodal stage (pN):
- N0: No cancer cells in lymph nodes.
- N1: Cancer cells in 1 to 3 lymph nodes.
- N2: Cancer cells in 4 or more lymph nodes.
What is the prognosis for a person with this tumour?
The prognosis is generally excellent, especially when the tumour is completely removed. Extended disease-free survival is common, even in patients with large tumours or limited metastases.
A small number of patients develop aggressive disease, usually when the tumour shows high-grade transformation. Because of this possibility, long-term follow-up is recommended for all patients.
Questions to ask your doctor
- Was my tumour completely removed?
- Did the tumour show any high-grade transformation?
- Is there evidence that the tumour spread outside the pancreas?
- What follow-up imaging will I need?
- What is the chance of recurrence in my case?
