What kind of appendix tumours
The appendix is a wormlike outpouching at the upstream end of the large intestine.
That means it is an outgrowth or protruding part between the small intestine (cecum) and large intestine (colon).
In pseudomyxoma peritonei (PMP), high grade lesions tend to grow quickly and patients are more likely to be offered chemotherapy. Low grade lesions grow more slowly and sometimes may be present for years without causing serious problems.
Because it is a small organ, cancer of the appendix is much less common than, say, cancer of the large intestine. However, it is prone to
specific types of tumour that are peculiar to it. We are going to focus on the tumours that can lead to PMP.
The main types of neoplasm arising in the appendix
Mucinous appendiceal neoplasms
These are the type that are the usual source of PMP.
Mucinous appendiceal neoplasms can cause a variety of symptoms, such as abdominal pain, bloating, and changes in bowel habits.
Goblet cell adenocarcinomas
Rare and occasionally show PMP-like spread.
These tumours are called “goblet cell” adenocarcinomas because they are made up of cells that resemble goblet cells, which are found in the lining of the digestive system and produce mucus.
Can spread to peritoneum but do not cause PMP.
Unlike mucinous adenocarcinomas, which are made up of cells that produce a lot of mucus, non-mucinous adenocarcinomas are made up of cells that do not produce mucus.
Mucinous appendiceal neoplasms
There are four main types of mucinous appendiceal neoplasm. They are classified by grade and type of invasion as shown in the table.
The commonest is LAMN and this tumour is the most frequent cause of PMP.
HAMN is rare. Despite its name, it is not as aggressive as mucinous adenocarcinoma, which by definition shows infiltrative invasion of
Signet ring cells are associated with poor prognosis statistically and have the highest grade.
|Type of appendiceal neoplasm||Cells||Type of invasion||WHO grading|
|1||Low-grade appendiceal mucinous neoplasm||Low grade||Pushing||G1|
|2||High-grade appendiceal mucinous neoplasm||High grade||Pushing||G2|
|3||Mucinous adenocarcimona||Any grade||Infiltrative||G2|
|4||Mucinous adenocarcimona with signet ring cells||Signet ring cells present||Infiltrative||G3|
When does pseudomyxoma peritonei occur?
Pseudomyxoma peritonei (PMP) occurs when cells from a mucinous appendiceal neoplasm enter the abdominal cavity.
The image is a low-power view of a section stained with haematoxylin and eosin. It shows an LAMN of the appendix that has ruptured due to pushing invasion through the appendiceal wall. The neoplastic cells can then escape into the abdomen, where they can grow and produce PMP. Neoplastic diseases are conditions that cause tumour growth.
Goblet cell adenocarcinomas
Goblet cell adenocarcinomas (GCA) were called “goblet cell carcinoids” for many years. This name was confusing because GCAs are a type of adenocarcinoma and are not part of the neuroendocrine tumour family. Thankfully, the WHO has now authorised a change in terminology to the more appropriate “GCA”.
GCAs are rare. They can spread to the peritoneum and can cause large Krukenberg tumours (a type of cancerous tumour that forms in the ovaries). They are sometimes treated with cytoreductive surgery and heated intraperitoneal chemotherapy.
Many classifications have been proposed for grading goblet cell adenocarcinomas. The Tang system was the main classification for many years, but the WHO has recently introduced a different system. The two classifications are contrasted in the table (Tang grades do not necessarily correspond to any particular WHO grade).
|A||The tumour cells stick together and look similar to each other, and there are not a lot of abnormal features or surrounding tissue growth.||G1||More than 75% of the tumour is made up of tubular or clustered growth|
|B||Unusual patterns or cell appearance||G2||About half to three-quarters of the growth is in the form of tubes or clusters|
|C||Areas where the cancer cells are close together and look like signet rings or areas where the cancer cells look very different.||G2||Less than half of the cells grow in clusters or tubules.|
Non-mucinous appendiceal adenocarcinoma
As elsewhere in the gut, adenocarcinomas are not called “mucinous” if less than 50% of the tumour consists of extracellular mucin.
Adenocarcinomas that are not mucinous are unusual in the appendix. They are less well understood than their mucinous counterparts. Grading uses the same terminology as colorectal adenocarcinomas.
Neuroendocrine tumours (NETs), previously known as “carcinoids”, are not uncommon in the appendix.
Almost all appendiceal NETs are G1 or G2. The most reliable indicator of metastatic potential is tumour size. Other features of the primary tumour have little if any association with prognosis.
Neuroendocrine carcinomas and mixed neuroendocrine non-neuroendocrine neoplasms (MiNENs) have been described in the appendix but are exceptionally rare.
- NETs have nothing to do with goblet cell adenocarcinomas
- The term “MiNEN” must not be used for goblet cell adenocarcinomas
Other types of appendix tumour
Gastrointestinal stromal tumour (GIST) of the appendix
Gastrointestinal stromal tumour (GIST) of the appendix is a very rare type of cancer that starts in the appendix, a small organ attached to the large intestine. GISTs are tumours that arise from specialized cells in the digestive system called interstitial cells of Cajal, which help regulate digestive function.
Interstitial cells of Cajal (ICC) are specialised cells found in the digestive system that help to regulate the muscular contractions that move food through the digestive tract. ICC are often referred to as the “pacemaker cells” of the digestive system, as they generate electrical signals that help to coordinate and synchronize the rhythmic contractions of the smooth muscle that lines the digestive organs.
GISTs can cause symptoms such as abdominal pain, nausea, vomiting, and changes in bowel habits. Treatment typically involves surgery to remove the tumour and any affected surrounding tissue, followed by targeted therapy with drugs that specifically target the abnormal proteins that are driving the growth of the tumour.
The prognosis for GISTs of the appendix varies depending on the stage of the tumour, but early diagnosis and treatment can improve outcomes. It is important to consult a doctor if you experience any persistent or unusual symptoms, as early diagnosis and treatment can be crucial in fighting this type of cancer.
Primary lymphoma of the appendix
Primary lymphoma of the appendix is a rare type of lymphoma or cancer that develops in the appendix. Normally, the appendix does not contain any lymphatic tissue (collections of lymphatic cells, lymph nodes, lymph tissue, and lymphocytes found throughout the body). However, in some people the appendix can develop its own lymphatic tissue and harbour lymphoma cells. When lymphoma originates in the appendix, it is known as primary lymphoma of the appendix.
This type of lymphoma causes symptoms like abdominal pain, swelling, or an abdominal mass, similar to appendicitis. It can mimic a condition like an inflamed appendix, delaying an accurate diagnosis. Because it develops from the appendix, it is considered a primary gastrointestinal lymphoma.
Gangliocytic paraganglioma of the appendix
YGangliocytic paraganglioma of the appendix is an extremely rare tumour. Gangliocytic paraganglioma develops from the tissue lining the appendix. It emerges from neuroendocrine cells that normally produce hormones to regulate digestion and the intestines. In this tumour, these cells become overactive and lead to uncontrolled growth of tissue.
Because it is so rare, not much is known about what causes this tumour or its exact biological behaviour. It grows slowly, considered benign yet it can occasionally metastasize to regional lymph nodes, as well as to distant organs.
Granular cell tumour of the appendix
Granular cell tumour of the appendix is a rare benign tumour. Granular cell tumours develop from Schwann cells, which are cells that form a protective coating around nerves. In the appendix, these cells can become overactive and form benign tumours.
These tumours are non-cancerous growths, though they may cause symptoms like abdominal pain, swelling or changes in bowel habits that lead to discovery and removal of the appendix. They are usually found incidentally during surgery for another condition.
Appendiceal Collision Tumour
A collision tumour refers to the simultaneous appearance of two adjacent but distinct malignant neoplasms in the same organ.
They arise from two separate primary tumours that happen to develop close together, rather than one tumour differentiating into two types. They are considered distinct primary tumours.
The two tumour components in a collision neoplasm often have different histological types, grading, and staging. For example, one could be low-grade appendiceal mucinous adenocarcinoma and the other neuroendocrine tumour.
Collision neoplasms are rare, making up only about 1-2% of all malignant tumours. A literature review has revealed only a few documented cases of appendiceal collision tumours. They are considered a diagnostic curiosity.
Collision neoplasms are not to be confused with divergent pathology.
The pathology of pseudomyxoma peritonei and appendix tumours
Pseudomyxoma Survivor and N Carr, MB BS FRCPath FRCPA FAcadMEd, Pseudomyxoma Survivor website, 2023
A Consensus for Classification and Pathologic Reporting of Pseudomyxoma Peritonei and Associated Appendiceal Neoplasia
Carr, Norman J. FRCPath; Cecil, Thomas D. MD; Mohamed, Faheez; Sobin, Leslie H.; Sugarbaker, Paul H.; González-Moreno, Santiago MD PhD; Taflampas, Panos MD; Chapman, Sara PhD; Moran, Brendan J. MD, A Consensus for Classification and Pathologic Reporting of Pseudomyxoma Peritonei and Associated Appendiceal Neoplasia, The American Journal of Surgical Pathology: January 2016 – Volume 40 – Issue 1 – p 14-26 doi: 10.1097/PAS.0000000000000535
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Pseudomyxoma peritonei (PMP)
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Primary signet ring cell carcinoma of the appendix: a rare case report and our 18-year experience
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Primary lymphoma of appendix presenting as acute appendicitis...
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Gangliocytic paraganglioma of the appendix - sages abstract archives
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Granular cell tumor of the appendix...
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The appendix: A rare case of an appendiceal collision tumor
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