Appendix cancer and appendiceal tumours

How an appendix tumour is found

It is rare. Tumours turn up in roughly 1–2% of the appendices removed, and population incidence sits at approximately one to two cases per hundred thousand people per year, with an upward trend over recent decades that is partly explained by better diagnosis and better classification.

There are three routes to the diagnosis. The commonest is the one you have just read: an appendicitis, an appendicectomy and a report that arrives two weeks later with an unfamiliar word on it. The second is a CT scan requested for another reason that shows the appendix dilated and full of mucus — a mucocele — or mucus and fluid spread around the abdomen. The third is an operation for something else, an inguinal hernia or a caesarean section, in which mucus appears where there should be none.

In all three cases the situation is the same: you have a report with a name you were not expecting, and what happens next depends on which name it is.

Frequency in appendicectomy specimens and population incidence: approximate figures from the PSOGI/EURACAN review (Govaerts K, et al. Eur J Surg Oncol 2021) and the population series it cites.

What the report says: the tumour types

For years every hospital called these tumours something different, and a patient could be given three names for the same lesion depending on who looked at the slides. In 2016 the Peritoneal Surface Oncology Group International, PSOGI, agreed a single classification, and it is the one that should appear in your report. In plain words:

• LAMN, low-grade appendiceal mucinous neoplasm. Cells that produce mucus and push against the appendix wall without truly invading it. They do not metastasise to lymph nodes or through the bloodstream. Their only danger is breaching the wall and seeding the peritoneum with mucus containing cells: that is pseudomyxoma.
• HAMN, high-grade appendiceal mucinous neoplasm. The same architecture, with cells that look more aggressive under the microscope. It is uncommon and handled with more caution, but as long as there is no invasion it is still not an adenocarcinoma.
• Mucinous adenocarcinoma. Here there is invasion of the wall. It is graded as well, moderately or poorly differentiated, and the report notes whether there are signet ring cells, the variant with the worst behaviour. It can metastasise to lymph nodes and behaves like a cancer.
• Goblet cell adenocarcinoma. It used to be called “goblet cell carcinoid”, and the old name was misleading because it suggested a neuroendocrine tumour with a good prognosis. It is not one: it behaves like an adenocarcinoma, with a tendency to spread to the peritoneum and, in women, to the ovaries.
• Neuroendocrine tumour, NET, formerly “carcinoid”. The commonest tumour of the appendix, almost always small, at the tip, and cured by the appendicectomy. What decides whether anything more is needed is its size and a few details in the report.

PSOGI classification: Carr NJ, et al. Am J Surg Pathol 2016. Current name for goblet cell adenocarcinoma: WHO Classification of Tumours of the Digestive System, 5th edition, 2019.

A LAMN with mucus outside the appendix: why it matters even when you feel well

The sentence in the report that changes the most decisions is not the name of the tumour. It is whether the mucus has left the appendix, and whether there are cells in that mucus.

A LAMN confined within the wall, with clear margins, is cured by the appendicectomy. In the largest series devoted to this question, no patient whose tumour was limited to the appendix recurred.

If the appendix ruptured and there is mucus outside it, but the pathologist finds no cells in that mucus, the risk of peritoneal disease appearing later is low — of the order of a few cases in a hundred. If there are tumour cells in the mucus, the risk rises sharply: in published series, around a third of those patients or more develop pseudomyxoma over the following years.

Here is the trap. That patient feels perfectly well. They have had an operation for appendicitis, they have recovered and the report arrives once they are back at work. That is exactly the moment when a call to a peritoneal surgery unit changes the course, because peritoneal disease visible on a CT scan is already bulk disease, and disease caught earlier is treated better. The pseudomyxoma that begins as a film of mucus in the right iliac fossa and the one discovered when the abdomen has grown are the same disease at two different moments.

And a word about the report itself: telling a LAMN from an adenocarcinoma, and saying whether the mucus outside does or does not contain cells, requires embedding the whole appendix and often cutting additional sections. A pathologist who sees one tumour-bearing appendix a year does not have the same hand as one who sees them every week. Asking for a second reading of the slides at an experienced centre is not distrust of anyone: it is what the consensus documents recommend.

No recurrence in LAMN confined to the appendix: Pai RK, et al. Am J Surg Pathol 2009 (116 cases). Risk according to whether extra-appendiceal mucin is acellular or cellular: Yantiss RK, et al. Am J Surg Pathol 2009; figures rounded for caution. Recommendation for specialist pathology review: Chicago Consensus 2020 and PSOGI/EURACAN 2021.

If the tumour was confined to the appendix: surveillance

When the LAMN has not breached the wall and the margins are clear, no further surgery is needed. What is needed is sensible surveillance, neither absent nor obsessive.

It consists of three things: a CT of the abdomen and pelvis at intervals, three blood markers — CEA, CA 19-9 and CA 125 — and someone who reads them with judgement. The markers are requested because, in this disease, they tend to rise when mucus containing cells is growing across the peritoneum, and because their baseline value serves as a reference. A normal marker rules nothing out and a raised one confirms nothing: they are an alarm, not a diagnosis.

The duration is long, because pseudomyxoma is slow. The international consensus documents recommend keeping up follow-up for years, more intensively when mucus had left the appendix and less so when it was contained. The exact interval should be set by the unit following you, and depends on what the pathologist found.

A small neuroendocrine tumour, under one centimetre, without deep invasion of the mesoappendix and with clear margins, does not need even that: the appendicectomy is curative and the guidelines recommend no follow-up.

Surveillance strategy and markers: Chicago Consensus Working Group, Cancer 2020; Govaerts K, et al. Eur J Surg Oncol 2021 (PSOGI/EURACAN). Appendiceal NET under 1 cm: ENETS guidelines (Pape UF, et al. Neuroendocrinology 2016).

When the colon must be removed, and when it must not

A right hemicolectomy — removing the last stretch of small bowel, the caecum and the right half of the colon with its lymph nodes — is the standard operation for right-sided colon cancer. And it is the first thing many surgeons think of when an appendix report says “tumour”. It is not always indicated, and doing it when it is not is not harmless.

It is indicated when the tumour may have travelled to the lymph nodes: in adenocarcinoma, in goblet cell adenocarcinoma, when there are positive nodes or an involved margin at the base of the appendix, and in a neuroendocrine tumour larger than two centimetres or with risk features in the report, such as deep invasion of the mesoappendix or involvement of the base.

It is not indicated in a LAMN. A LAMN does not metastasise to lymph nodes, and removing the colon does not remove a disease nobody has. This was shown more than twenty years ago in patients with mucinous peritoneal disease: right hemicolectomy did not improve survival compared with appendicectomy alone. What it does add is an anastomosis, one more scar on the peritoneum and, if a cytoreduction is needed later, an abdomen that is harder to operate on.

And if the tumour has already spread to the peritoneum, the question changes: the hemicolectomy stops being an isolated decision and becomes a part — or not — of the cytoreduction. That is decided by the peritoneal surgeon during the operation, not by the appendicectomy report.

Indications for right hemicolectomy by histology: Chicago Consensus Working Group, Cancer 2020; Govaerts K, et al. Eur J Surg Oncol 2021. No benefit in mucinous disease with peritoneal seeding: González-Moreno S, Sugarbaker PH. Br J Surg 2004. NET: ENETS guidelines 2016.

When the peritoneum is involved

There are two very different ways an appendix tumour can involve the peritoneum, and they should not be confused.

The first is pseudomyxoma peritonei: mucus containing low-grade cells that spreads through the cavity and gradually takes up room, without invading organs or leaving the abdomen. It is the commonest form, the one with the best prognosis, and the one with its own page on this site. Here the figure that sums it up is enough: in the pooled analysis of 2,298 patients treated with cytoreductive surgery and HIPEC at sixteen centres, median survival was 196 months and 63% were alive at ten years.

The second is high-grade carcinomatosis: a poorly differentiated mucinous adenocarcinoma, with or without signet ring cells, or a goblet cell adenocarcinoma that has seeded the peritoneum. Same cavity, same surgical technique, different biology. These cells invade, can reach lymph nodes and grow fast.

The results of cytoreductive surgery with HIPEC are different too. In the analysis of 2,298 patients, high-grade histology was one of the independent factors for worse survival, alongside incomplete cytoreduction, major complications and prior chemotherapy. In series devoted to high-grade disease, medians run in the order of two to four years and five-year survival sits well below that of low-grade disease, with the signet ring variant at the worst end. These are approximate figures and they vary between centres; what does not vary is the direction.

That does not mean surgery is not offered. It means selection is stricter: the disease has to be completely resectable, there must be no extensive nodal involvement or metastases outside the abdomen, and you must be fit for a long operation. In high-grade disease a high PCI does weigh against surgery; in low-grade disease, barely.

Pooled analysis of 2,298 patients: Chua TC, et al. J Clin Oncol 2012. Worse prognosis of high-grade and signet ring histology: same analysis and PSOGI/EURACAN guidelines 2021. Survival ranges in high-grade disease are given approximately because published series do not define grade in the same way.

The role of chemotherapy

In low-grade disease, systemic chemotherapy has no proven benefit. Pseudomyxoma cells divide slowly, and drugs that attack dividing cells have little to act on. In the pooled analysis, having received chemotherapy before surgery was independently associated with worse survival, and a small randomised trial published in 2024 in metastatic low-grade mucinous adenocarcinoma did not find that chemotherapy slowed the disease. If you have a LAMN or a low-grade pseudomyxoma and the plan you are offered begins with chemotherapy, ask for a surgical assessment first.

In high-grade disease the logic is that of colon cancer. Guidelines recommend treating advanced appendiceal adenocarcinoma with colorectal cancer regimens, before or after surgery, or instead of it when the disease is not resectable. Appendix-specific evidence is thin, because the disease is rare and has almost never had trials of its own, so it is borrowed. It is a board decision, with medical oncology, case by case.

Prior chemotherapy as an independent predictor: Chua TC, et al. J Clin Oncol 2012. Randomised crossover trial in low-grade disease: Shen JP, et al. JAMA Network Open 2024. Treatment of appendiceal adenocarcinoma with colorectal regimens: NCCN Colon Cancer guidelines (appendiceal adenocarcinoma section); Chicago Consensus 2020.

Why the first operation matters, and what not to do afterwards

The peritoneum has a memory. Every operation leaves adhesions and scars, and every scar is a place where mucus cells stick and where it is later harder to see and to clear. That is why, in this disease, the worst possible sequence is an appendicectomy followed by an improvised second operation at the same hospital — “to take a look” or “to remove the colon just in case” — and then a third at a specialist centre to do what needed doing.

If during the appendicectomy the surgeon finds mucus outside the appendix, the right thing is to remove the appendix whole without rupturing it, describe in detail where the mucus is, take a sample and close. Not to attempt to clear the abdomen without the technique or the team, and not to perform resections that were never planned. A detailed operative note is worth more than an ambitious operation done by halves.

When the finding was incidental and imaging shows no disease, there are two reasonable strategies. One is the surveillance with CT and markers you read about above. The other, in selected patients with cellular mucus outside the appendix, is a planned laparoscopy at a peritoneal unit a few months later, to look directly and treat whatever is there while it is still little. Which of the two suits you is decided by the unit with the report in front of them, not by a generic protocol.

For that assessment, what you need to bring is specific: the slides or the paraffin block from the appendicectomy, so a pathologist experienced in appendix tumours can review them; the full operative note, with the description of what the surgeon saw and not just the conclusion; and the imaging in digital form — the whole study, not the report. With those three things a decision can be made; without them, it is a guess.

Intraoperative management of the incidental finding and referral to a specialist unit: Chicago Consensus Working Group, Cancer 2020; Govaerts K, et al. Eur J Surg Oncol 2021. The author's practice.

What this page does not do

The figures you have read are percentages from groups of patients treated at experienced centres, and several are approximate because the disease is rare and the series are small. They do not describe your case.

And this page is no substitute for someone looking at your slides. Almost everything decided here depends on details of the pathology report that cannot be assessed from a screen: whether there is invasion, whether there are cells in the mucus, what grade, what margin. With the report in hand, at a unit that treats this disease, the conversation is a different one.