Papillary Mesothelioma

The primary characteristics of well-differentiated papillary mesothelioma are described right in the disease’s name. The phrase well-differentiated refers to the tumor’s grade, which doctors use to describe how quickly a tumor is expected to grow and spread. Well-differentiated tumors are low grade, meaning their cancer cells resemble healthy cells and grow and multiply at a slow rate. The cancer does not invade nearby tissues or spread throughout the body. In many cases WDPM is completely inactive, showing no signs of cell division.

The word papillary describes the microscopic growth pattern of the tumor’s cells, which features small finger-like projections called papillae. These projections are lined by a single layer of flat mesothelial cells and can appear uniform, coarse or branching. The papillae sometimes create round swirls of calcium known as psammoma bodies.

To the naked eye, WDPM tumors form white or grey nodules ranging from less than 1 centimeter in size to more than 3 centimeters. The tumors are smaller than 1 centimeter in more than half of all cases. WDPM can develop as a solitary mass or arise in many sites, the latter being known for more aggressive behavior.

Because well-differentiated papillary mesothelioma rarely causes symptoms, doctors usually discover tumor growth incidentally during an unrelated pelvic or abdominal surgery. WDPM can sometimes be found with an imaging test like a CT scan, but this technique isn’t sensitive enough to detect tumors smaller than 1 centimeter in size.

The only definitive procedure for diagnosing WDPM and other mesotheliomas is biopsy, the collection of a tissue sample for laboratory analysis. It is important for doctors to collect a comprehensive sample to prevent misdiagnosis because highly aggressive malignant mesothelioma tumors sometimes feature areas of papillary cell growth. Other indications that a suspected WDPM is actually malignant mesothelioma include tumor invasion of underlying tissue and a rapid progression of disease.

Doctors may confuse WDPM with several other cancers and conditions:

• Reactive mesothelial hyperplasia
• Adenomatoid tumor
• Peritoneal carcinomatosis
• Tuberculous peritonitis
• Serous papillary carcinoma of the ovary
• Serous papillary carcinoma of the peritoneum

If doctors make an inaccurate diagnosis, patients may receive aggressive treatments that do not improve the outcome of WDPM. Another way doctors can prevent misdiagnosis is by collecting blood or fluid samples from patients and testing for certain biomarkers associated with the disease. Well-differentiated papillary mesothelioma will test negative for carcinoembryonic antigen (CEA) and positive for the markers cytokeratin (CK), calretinin and HMBE-1.

With only a limited amount of research on the management of well-differentiated papillary mesothelioma, doctors have yet to reach a consensus on the most effective course of treatment. Therapy usually involves some combination of the main types of mesothelioma treatment:

• Surgery
• Chemotherapy
• Radiation Therapy

The first procedure that most peritoneal WDPM patients receive is an exploratory laparotomy. In this type of surgery, doctors make a large incision in the patient’s abdomen to determine a diagnosis or perform cytoreductive surgery, which aims to remove most of the tumor. Some physicians, however, claim that laparotomy is too risky for an unaggressive cancer like WDPM, and instead prefer a series of biopsies to make an accurate diagnosis.

Various approaches to chemotherapy have been explored for WDPM treatment. One patient with WDPM tumors of both the pleura and peritoneum was successfully treated with carboplatin. The drug was administered intravenously and also injected directly into the pleural and peritoneal cavities. One year after diagnosis the patient showed no signs of disease.

Several patients have been given radiation therapy after a primary treatment of chemotherapy, but some doctors state this method should be avoided unless there are clear signs of cancer progression. In one study of 22 cases of well-differentiated papillary mesothelioma of the peritoneum, several patients given this therapy did not survive. The doctors could not determine if the tumor was the cause of death for these patients.

Some WDPM patients have also received cytoreductive surgery followed by heated chemotherapy with mixed results. This treatment involves heating chemotherapy drugs slightly higher than the patient’s body temperature to improve the treatment’s effectiveness. One patient treated with this method survived 15 months after the therapy and another was alive 40 months later. A third patient died of disease progression 13 months after treatment.

Researchers hope additional data on well-differentiated papillary mesothelioma gained from long-term follow-ups and additional studies will eventually reveal the optimal treatment plan for the disease.