There are an estimated 300 million people living with a rare disease and there are over 200 rare cancers globally. To raise awareness for those affected by these rare disorders and to support Rare Disease Day – 28 February 2022 – this article focusses on an extremely rare cancer known as pseudomyxoma peritonei (PMP).
PMP is a malignant disorder of the abdomen and pelvis characterised by the progressive accumulation of mucinous tumour cells . The annual incidence of PMP is estimated at just 1–2 cases per million people [1–3]. It often presents with non-specific signs and symptoms and is therefore commonly misdiagnosed or identified at an advanced stage . Although the rate of progression in PMP can vary, it is generally slower than other abdominal malignancies . However, despite its indolent nature, PMP is a debilitating disorder that can greatly impair the quality of life of affected patients; therefore, early diagnosis and treatment initiation are critical . This article will provide an overview of the pathogenesis, clinical presentation, diagnosis, and treatment of PMP.
PMP is not associated with any environmental or genetic factors, and the exact cause of the disorder is currently unknown .
PMP begins with neoplastic transformation of cells in the appendix and formation of a small tumour . Growth of the tumour eventually causes a small perforation or rupture in the wall of the appendix, allowing mucinous tumour cells to enter the peritoneal cavity [1, 2]. These tumour cells subsequently circulate in the peritoneal fluid and disseminate throughout the peritoneal cavity, accumulating at sites such as the greater omentum (the membrane in front of the intestines), the diaphragm, and within the pelvis and the ovaries [1, 2]. Mucin secretion from the tumour cells increases intra-abdominal pressure and compression of visceral organs, which results in many of the symptoms that are characteristic of PMP [1, 2].
Disease onset typically occurs in the fifth decade of life, and the average age at diagnosis is 53 years [1, 2]. It has been reported that PMP is more common in women, although this may be due to misdiagnosis of ovarian tumours [2, 3].
The most common presenting symptoms in patients with PMP are abdominal distension and ascites (often referred to as a ‘jelly belly’), which increase intra-abdominal pressure, leading to abdominal discomfort [1, 2]. Women with PMP may also present with an enlarged ovary, whereas hernias in the lower abdomen or groin area (known as inguinal hernias) are often seen in men . Other symptoms include changes in bowel habits, loss of appetite, and difficulties becoming pregnant . If left untreated, mucin accumulation can promote inflammation and fibrosis, potentially leading to intestinal obstruction, which can be fatal [1, 5].
Figure 1: The early stage of PMP is characterised by cells leaving the primary tumour and entering the peritoneal cavity. Tumour cells circulate throughout the peritoneal cavity with the peritoneal fluid, producing mucin (A). During late-stage PMP, tumour cells adhere at sites throughout the peritoneum and proliferate. This leads to tumour growth, continued mucin accumulation, inflammation, and fibrosis (B). (Adapted from Encyclopedia. Pseudomyxoma peritonei ).
PMP is usually diagnosed through imaging of the abdomen and pelvis via computed tomography (CT) or magnetic resonance imaging (MRI) to investigate the distribution and accumulation of mucin [1, 2]. Circulating tumour markers, such as carcinoembryonic antigen (CEA) and carbohydrate antigen 19.9 (CA19.9), may also direct PMP diagnosis and prognosis, and they are therefore tracked during postoperative follow-up . Histopathological examination of a biopsy sample may be required to confirm diagnosis in some patients [6, 7]. The tissue sample may be acquired during keyhole surgery (laparoscopy), or via a CT or ultrasound guided biopsy . Alternatively, PMP is incidentally identified in up to 20% of patients during investigations or procedures for other conditions (e.g. laparotomy, laparoscopy) .
As the symptoms of PMP are often non-specific, it can be mistaken for other abdominal malignancies, including mucinous cancers of the ovary, colon, stomach, and gallbladder . Other conditions that might be confused with PMP include ascites originating from cirrhosis, endometriosis, mesothelioma, and acute inflammatory conditions of the appendix [1, 6, 8].
The current standard of care for PMP is cytoreductive surgery (CRS) combined with hyperthermic intraperitoneal chemotherapy (HIPEC) .
CRS is performed with peritonectomy to remove or destroy all visible tumours within the peritoneal cavity [1, 6]. Following CRS, HIPEC is performed; chemotherapy (typically mitomycin C) is administered directly into the peritoneal cavity for 90 minutes to remove any viable macro- or microscopic tumour residues and prevent the reimplantation of cancer cells [1, 6, 9]. The mitomycin C is heated to 41°C, which improves drug penetration and local cytotoxicity .
CRS-HIPEC is an aggressive and long procedure (lasting up to 12 hours) . However, the outcome is often positive, with a 5-year survival rate of up to 86% and median survival and median progression-free survival rates of 16.3 years and 8.2 years, respectively [2, 5, 10]. Some patients may undergo debulking surgery for partial, rather than complete, removal of cancerous tissue; although this procedure will not cure PMP, it may reduce symptom burden and facilitate the use of HIPEC in the future . Abdominopelvic radiotherapy may be used as a palliative therapy .
Access to specialist consultants and facilities is an important determinant of prognosis in patients with PMP . In line with this, the National Institute for Health and Care Excellence (NICE) currently recommends that patients with PMP in the UK are treated at one of the two designated specialist treatment centres :
- The Peritoneal Malignancy Institute at Basingstoke and North Hampshire NHS Foundation Trust
- The Colorectal and Peritoneal Oncology Centre at The Christie Hospital in Manchester
PMP is a rare condition with a non-specific presentation that often leads to misdiagnosis and delays in treatment. Greater awareness and understanding among patients and healthcare professionals may facilitate earlier identification of the signs and symptoms of PMP, allowing patients to receive the correct diagnosis and appropriate treatment as early as possible.
The information in this article is not intended or implied to be a substitute for professional medical advice, diagnosis or treatment. All content is for general information purposes only. Always seek the guidance of your doctor or other qualified healthcare professional with any questions you may have regarding your health or medical condition.
For more information on rare diseases and why it is important to raise awareness of these diverse group of disorders, read our article: https://www.porterhousemedical.com/news/why-is-it-important-to-raise-awareness-of-rare-diseases
- National Organization for Rare Disorders. Pseudomyxoma peritonei. Available at: https://rarediseases.org/rare-diseases/pseudomyxoma-peritonei/. Accessed February 2022.
- Amini A, Masoumi-Moghaddam S, Ehteda A et al. Secreted mucins in pseudomyxoma peritonei: Pathophysiological significance and potential therapeutic prospects. Orphanet J Rare Dis 2014; 9: 71.
- Pseudomyxoma peritonei. Available at: https://www.orpha.net/consor/cgi-bin/OC_Exp.php?Expert=26790&lng=EN. Accessed February 2022.
- Cancer Research UK. About pseudomyxoma peritonei. Available at: https://www.cancerresearchuk.org/about-cancer/pseudomyxoma-peritonei/about. Accessed February 2022.
- Pseudomyxoma peritonei. Available at: https://encyclopedia.pub/6694. Accessed February 2022.
- National Center for Biotechnology Information. Pseudomyxoma peritonei. Available at: https://www.ncbi.nlm.nih.gov/books/NBK541116/. Accessed February 2022.
- Macmillan Cancer Support. Pseudomyxoma peritonei (PMP). Available at: https://www.macmillan.org.uk/cancer-information-and-support/bowel-cancer/pseudomyxoma-peritonei. Accessed February 2022.
- Buell-Gutbrod R and Gwin K. Pathologic diagnosis, origin, and natural history of pseudomyxoma peritonei. Am Soc Clin Oncol Educ Book 2013; 221–225.
- The Christie NHS Foundation Trust. About the condition. Available at: https://www.christie.nhs.uk/patients-and-visitors/services/colorectal-and-peritoneal-oncology-centre/information-for-professionals/about-the-condition. Accessed February 2022.
- Zhong Y, Deng M, Xu R et al. Pseudomyxoma peritonei as an intractable disease and its preoperative assessment to help improve prognosis after surgery: A review of the literature. Intractable Rare Dis Res 2012; 1 (3): 115–121.
- Cancer Research UK. Treatment for pseudomyxoma peritonei. Available at: https://www.cancerresearchuk.org/about-cancer/pseudomyxoma-peritonei/treatment. Accessed February 2022.
Author: Tom O’Sullivan, PhD
Medical Writer | Pronouns: He/Him | Porterhouse Medical