Pseudomyxoma peritonei (PMP) is a clinical condition caused by cancerous cells (mucinous adenocarcinoma) that produce abundant mucin or gelatinous ascites. The tumors cause fibrosis of tissues and impede digestion or organ function, and if left untreated, the tumors and mucin they produce will fill the abdominal cavity. This will result in compression of organs and will destroy the function of the colon, small intestine, stomach, or other organs. Prognosis with treatment in many cases is optimistic, but the disease is lethal if untreated, with death occurring via cachexia, bowel obstruction, or other types of complications. This disease is most commonly caused by an appendiceal primary cancer (cancer of the appendix); mucinous tumors of the ovary have also been implicated, although in most cases ovarian involvement is favored to be a metastasis from an appendiceal or other gastrointestinal source. Disease is typically classified as low- or high-grade (with signet ring cells). When disease presents with low-grade histologic features the cancer rarely spreads through the lymphatic system or through the bloodstream.
Signs and symptoms Signs and symptoms of pseudomyxoma peritonei may include abdominal or pelvic pain and/or bloating, distension, digestive disorders, weight changes, increased girth, and infertility.
Cause The primary tumor appears to arise from the MUC2-expressing goblet cells and most commonly from these cells in the appendix. The KRAS and p53 genes may be involved in the oncogenesis. It may be diagnosed with a range of conditions. While the majority of these cases are associated with appendiceal carcinomas, other conditions may also be found, including disseminated peritoneal adenomucinosis (DPAM), peritoneal carcinomas, several mucinous tumors (mucinous adenocarcinoma, mucinous cystadenoma, and mucinous cystadenocarcinoma), as well as other disease states. Other primary sites that have been reported include colon, rectum, stomach, gallbladder, bile ducts, small intestine, urinary bladder, lung, breast, fallopian tubes, and the pancreas.
Diagnosis This disease is often discovered during surgery for other conditions, e.g., hernia repair, following which an experienced pathologist can confirm the diagnosis. Advanced stages may present as tumors palpable on the abdomen or distention of the belly ("jelly belly" is sometimes used as a slang term for the condition). Due to the rarity of this disease, it is important to obtain an accurate diagnosis so that appropriate treatment may be obtained from a gastrointestinal cancer surgeon. Diagnostic tests may include CT scans, examination of tissue samples obtained through laparoscopy, and the evaluation of tumor markers. In most cases, a colonoscopy is unsuitable as a diagnostic tool, because, in most cases, appendix cancer invades the abdominal cavity but not the colon (however, spread inside the colon is occasionally reported). PET scans may be used to evaluate high-grade mucinous adenocarcinoma, but this test is not reliable for detecting low-grade tumors, because those do not take up the dye which shows up on scans. New MRI procedures are being developed for disease monitoring, but standard MRIs are not typically used as a diagnostic tool. Diagnosis is confirmed through pathology.
Classification There is substantial debate regarding histopathologic classification of pseudomyxoma peritonei. In 1995, Ronnett et al. proposed separating pseudomyxoma peritonei cases into two diagnostic categories: adenoma (disseminated peritoneal adenomucinosis, DPAM) or carcinoma (peritoneal mucinous carcinomatosis, PMCA) with a third category reserved for cases with intermediate features. In this classification system, cases of DPAM were characterized by peritoneal lesions composed of abundant extracellular mucin containing scant simple to focally proliferative mucinous epithelium with little cytologic atypia or mitotic activity (in other words, most cells looked fairly normal and there was no evidence of mitosis which would indicate that cells were rapidly dividing), with or without an associated appendiceal mucinous adenoma. Cases of PMCA were characterized by peritoneal lesions composed of more abundant mucinous epithelium with the architectural and cytologic features of carcinoma (irregular cells, evidence that cells were rapidly dividing, and other criteria), with or without an associated primary mucinous adenocarcinoma. Bradley et al. (2007) argued that continued use of non-malignant terms, i.e., adenoma, for those frequent cases with low-grade features (such as DPAM), is misleading because pseudomyxoma peritonei is a disease state that results from invasion of the abdominal cavity by cells with uncontrolled growth. Bradley states that an adenoma, by definition, is a tumor confined to the appendiceal mucosa with absolutely no evidence of invasion beyond the muscularis mucosae. The term mucinous adenocarcinoma is used in different contexts depending on the reference material used by the pathologist for disease classification. For example, neoplasms characterized by high-grade features, invasive glands and or signet ring cells, are termed adenocarcinoma in pathology literature. However, some pathologists (e.g., Odze and Goldblum, Surgical Pathology of the GI Tract, Liver, Biliary Tract and Pancreas, 2nd ed.) also use the term mucinous adenocarcinoma when referring to low-grade, well-differentiated tumors lacking high-grade features. Low-grade mucinous adenocarcinoma is used by the American Joint Committee on Cancer and World Health Organization and is nearly or completely synonymous with the DPAM designation. For low-grade mucinous adenocarcinoma, disease may be designated as "benign" because tumors do not invade deeply into tissue and rarely metastasize to parenchyma of organs; this designation may be misleading and confusing to the layperson because pseudomyxoma peritonei is not a harmless condition, fatal if untreated. High-grade or poorly differentiated mucinous adenocarcinoma has a generally poorer prognosis, though surgical treatment with heated intra-peritoneal chemotherapy (HIPEC) is yielding promising outcomes (see surgical treatment).
Immunohistochemistry Immunohistochemical features:
Diffuse expression of SATB2, CK20, CDX2, and mCEA Sometimes patchy CK7; negative PAX8 High-grade neoplasms may show loss of DPC4 (10%)
… excerpt ends here. Continue reading the full article.
