A papillary mesothelial tumor is a growth that arises from the mesothelium, a thin layer of tissue that lines and protects most of the body’s internal organs. These tumors are uncommon and represent a category separate from the more aggressive cancer called malignant mesothelioma. While the term can cause concern, it describes a growth that is often benign or slow-growing.
These growths get their name from their unique structure. The term “papillary” refers to the small, finger-like projections that characterize the tumor’s surface when viewed under a microscope. This cellular arrangement gives it a distinct appearance that pathologists use for identification.
Tumor Characteristics and Common Locations
The defining feature of a papillary mesothelial tumor is its microscopic structure, composed of small, branching projections called papillae. These can sometimes form round swirls of calcium deposits called psammoma bodies. Visually, the tumors appear as small, whitish or grey nodules, which can range from less than a centimeter to over three centimeters. In many instances, these tumors do not invade nearby tissues, a characteristic that sets them apart from more aggressive cancers.
These tumors develop on the mesothelium, the protective membrane covering internal organs. The most common site is the peritoneum, the membrane lining the abdominal cavity, but they can also occur in the pleura (lining the lungs), the pericardium (around the heart), or the tunica vaginalis (surrounding the testes). They are most frequently identified in the peritoneum, particularly in women.
Distinguishing Benign and Malignant Forms
Papillary mesothelial growths exist on a spectrum. Many are classified as papillary mesothelial hyperplasia, a benign, non-cancerous condition that is an overgrowth of normal mesothelial cells. These are often discovered incidentally.
A distinct diagnosis is the Well-Differentiated Papillary Mesothelial Tumor (WDPMT), formerly known as WDPM. This tumor is considered to have low malignant potential, meaning it is a low-grade, slow-progressing tumor that is unlikely to spread aggressively.
The behavior of WDPMT stands in sharp contrast to malignant mesothelioma, a high-grade cancer characterized by rapid, invasive growth and a tendency to metastasize. Pathologists differentiate these tumors by examining cell structure and using special stains. For instance, in malignant mesothelioma, protein markers like BAP1 are often absent, whereas they are present in WDPMT.
The Diagnostic Process
Many papillary mesothelial tumors are found incidentally during imaging tests, such as a CT scan or ultrasound, performed for unrelated medical issues. In other cases, a person might experience vague symptoms like the buildup of fluid in the abdomen, known as ascites, which prompts investigation. While imaging can reveal the presence of nodules on the mesothelium, it cannot definitively identify the tumor type.
A definitive diagnosis requires a biopsy, which involves obtaining a tissue sample for laboratory analysis. The method for collecting this sample depends on the tumor’s location, such as a laparoscopy for the abdomen or a thoracoscopy for the chest cavity.
The collected tissue sample is sent to a pathologist for histopathological examination. This expert analysis of the tissue’s cellular architecture confirms the diagnosis, distinguishing between benign hyperplasia, a low-grade WDPMT, or malignant mesothelioma.
Treatment and Management Approaches
The management strategy for a papillary mesothelial tumor is tailored to its type, size, and whether it is causing symptoms. For small, asymptomatic tumors, particularly benign hyperplasia or WDPMT, doctors may recommend a “watchful waiting” approach. This involves active surveillance with periodic imaging scans to monitor the tumor for any changes.
When a tumor is larger, causes symptoms like pain or fluid buildup, or if there is uncertainty about its nature, surgical removal is the primary treatment. The objective of the surgery is cytoreduction, which means removing all visible signs of the tumor. Complete removal offers the best outcome for symptomatic patients.
In certain situations, such as widespread or recurrent disease, other treatments may be considered. One option is hyperthermic intraperitoneal chemotherapy (HIPEC), a procedure where heated chemotherapy drugs are circulated within the abdominal cavity after surgery. This technique targets any remaining microscopic cancer cells but is less frequently required for WDPMT than for more aggressive cancers.
Prognosis and Long-Term Outlook
The long-term outlook for individuals with papillary mesothelial tumors is generally favorable, especially for those with benign hyperplasia or WDPMT. Because these tumors are slow-growing and non-invasive, many people live for decades after their diagnosis. The prognosis is significantly better than that associated with malignant mesothelioma.
Despite the positive outlook, the potential for recurrence is an important consideration. Even when a WDPMT is completely removed, it can return, sometimes years later. This possibility requires long-term follow-up care with regular check-ups and imaging to monitor for any new growths and intervene early if needed.
The prognosis depends on several factors, including the extent of the tumor at diagnosis and the success of the surgical removal. A patient’s overall health also plays a role in the long-term outcome.