APPENDIX CANCER & Pseudomyxoma Peritonei (PMP)

Appendix cancer and PMP can be very confusing to understand.  Because they are rare, you may have no friends and family who can share their own experiences and help you understand your diagnosis.  Also, the terminology has been used inconsistently over the years, leading to patient confusion.  And, there are different forms of appendix cancer, and PMP is not present with all forms.  Read on to learn the basics and find helpful resources for more in-depth learning.


Appendix cancer starts in the part of your large intestine called the appendix. The large intestine (also called your “colon”) is located inside your abdominal area, known as the peritoneal cavity.  The peritoneum is the lining that surrounds this cavity and the many organs found there.

Appendix cancer starts by genetic mutation of some of the cells in the appendix.  The mutations typically result in abnormal cell growth and tumor production. The lining of the appendix contains epithelial cells, which produce mucin, as do similar cells in other parts of the colon. Mucin is a jelly-like substance that protects the lining of the intestines.  Even after genetic mutation, the epithelial cells of the appendix continue their mucin-producing function.

As the mutant cells and mucin accumulate inside the appendix and begin to press against its wall, the resulting tumor can break through the thin wall of the appendix. This breach allows the cells to enter the peritoneum, thus spreading to the lining of the abdominal cavity and to the surface of organs located there, such as the colon, the spleen, or the bladder.

Even when cancer cells spread to other organs, it is customary to continue to identify the cancer by the organ in which it originated.  Thus, it will be called “appendix cancer” because of where it originated and the biological make-up of the cells specific to the appendix.

Some tumors growing in the appendix never breach the wall of the organ.  They may be benign (not malignant), or they may be malignant in nature but too small to have broken through yet.  Often these tumors are discovered after a patient has an appendectomy, for example, and abnormal tissue from the appendix is analyzed by a pathology lab.  However, for many patients, appendix cancer is found after the appendix wall has been breached.  Treatment becomes more complicated after cancer cells move into the abdominal cavity. Once there, the cancer cells and the mucin can grow, spreading widely throughout the cavity and attaching to surfaces of the many organs in this part of the body.

A patient may experience growth of cancer cells in the abdominal cavity with or without the build up of mucinous fluid.  Many patients learn they have appendix cancer/PMP after years of growth but no symptoms at all – no pain, no bloating, no other problems.  For many, symptoms do eventually appear and lead to screening and a diagnosis; for others, there may be another event, such as perhaps surgery for a hernia, that leads to a discovery of the tumors and diagnosis.

There are several sub-types of appendix tumors.  For your physician to identify your sub-type and formulate an appropriate treatment plan, cell tissue is analyzed in a laboratory by a pathologist.  The tissue is obtained by either surgery, a laparoscopy, or a biopsy.  Once tissue samples are obtained and sent for analysis, your physician will receive a report that details the findings.  It is important for you to obtain each lab report and make it a part of your notebook containing your relevant medical records.


This is a rare condition characterized by a build-up of mucin in the peritoneal cavity.  PMP most commonly results from a ruptured, mucus-secreting appendix tumor, though there can be other causes. For example, PMP may be caused by other forms of cancer cells that have spread to the peritoneum, such as colon or ovarian cancer cells, or from conditions like mesothelioma.

Likewise, appendix cancer may be present with or without the spread of mucin in the peritoneal cavity.  Some forms of appendix cancer, such as neuroendocrine tumors, are present without the mucin build-up that characterizes PMP.

In the vast majority of cases, PMP does not spread beyond the peritoneal cavity.  It does not spread via the bloodstream or lymph systems as cancers normally will do.  Thus, it is debated as to whether it is truly malignant in nature.  Often it is referred to as “borderline malignant.”  Nevertheless, it can be a dangerous and fatal condition.  Large mucinous tumors can interfere with nutrition and compress other organs, making normal functionality impossible.  Large amounts of mucin and fluid can accumulate, referred to ascites, causing extreme distention, discomfort and pain.  The mucin typically will settle in certain parts of the peritoneal cavity in which fluids normally accumulate due to gravity and physiology, but it can also be found widely spread through the whole cavity.

PMP can vary from low grade (LAMN) to high grade (HAMN), meaning there are larger, more actively dividing cells.  Some patients have a more aggressive form of appendix cancer known as mucinous adenocarcinoma, which can include a highly aggressive form, signet ring cell.

For more, see below, Types of appendiceal tumors.  See also a good overview at NORD


Categorizing and naming the types of appendiceal tumors is a complex task.  Over the years, various terminology has been applied and then changed. Plus, surgeons and pathologists may be in the habit of using different terms to apply to the same type of tumor.  This makes it quite confusing for patients to understand the nature of their disease.

From a patient standpoint, it is critical to obtain your pathology reports after surgery or a biopsy.  These reports will provide a “name” for your sub-type of appendix cancer; with that, you then can research and develop a fuller understanding of your condition.  The pathology reports will help you understand your diagnosis.  Identification of the “histology” (i.e., the type of structure or features of the tissue being examined microscopically) also tells your physician more about how your cancer is likely to grow (prognosis) and the treatment it will best respond to.  Note that diagnostic imaging, such as a CT scan or MRI, cannot show the distinction between tumor types with certainty, though some imaging will suggest a certain pattern; cells must be sampled and analyzed under the microscope to be able to determine the type of tumor.

The chart below shows the types of tumors your physician may discuss with you.

Sub-Types of Appendiceal Cancers and Tumors

Another excellent source of information can be found in the PMP Pals HOPE ZOOM video library. HOPE ZOOM | PMP Pals . See the presentation by Dr. Joseph Misdraji on Pathology of PMP, June 18, 2020. Dr. Misdraji is a leading pathologist specializing in appendix cancer. He is joined in this presentation by Dr. Laura Lambert, a surgeon specializing in appendix cancer and other peritoneal surface malignancies. They answer many common questions from patients like you.

In addition to the tumor types above, you may also hear the terms below in regard to your condition; these terms may apply to the spread of disease from either appendix cancer or cancers of other origins:

PERITONEAL CARCINOMATOSIS, A condition associated with appendix cancer or other cancers originating in or near the peritoneal cavity.  Peritoneal carcinomatosis is characterized by the growth of cancer cells within the abdominal cavity.  This also is often referred to as “peritoneal surface malignancy (PSM).”

PERITONEAL SURFACE MALIGNANCY (PSM).  When cancer arises in an organ in the peritoneum (such as the appendix) or in the lining of the peritoneum itself and then spreads into the peritoneum, it is a peritoneal surface malignancy (PSM). This condition may or may not involve particular organs to which the malignancy has spread. For most patients who participate in PMP Pals, their disease has spread from the appendix to the peritoneum and is accompanied by the mucinous tumors known as PMP.   The term “peritoneal carcinomatosis” may be used interchangeably with PSM.


The information on the PMP Pals website relates primarily to appendix cancer produced by cells that are mucin-producing.  However, the appendix also contains cells that do not produce mucin; these are known as neuroendocrine cells.  In fact, the most common type of tumor or cancer beginning in the appendix is a neuroendocrine (also called carcinoid) tumor.  Specialized cells in the wall of the appendix can mutate and become NETs. 

These tumors have quite different histology (tumor biology) than the gland-forming epithelial cells that are mucin-producing.  Thus, treatment of patients with NETs is different from the treatment of patients with appendix cancer from epithelial, mucin-producing cells.  If you have been diagnosed with carcinoid tumors (NETs), please see these resources:  Neuroendocrine Tumor of the Gastrointestinal Tract: Types of Treatment | Cancer.Net, a detailed webpage maintained by the American Society of Clinical Oncology.  More information can be found at Carcinoid Tumor | Johns Hopkins Medicine