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Well-differentiated papillary mesothelioma, or WDPM, is a rare subtype of this type of cancer. Mesothelioma is most often associated with asbestos exposure, but WDPM may not be related to that risk factor at all. There have been only a couple hundred cases of this type of mesothelioma ever described or studied, so the information about what causes it is limited.

What is known is that WDPM is a subtype of the epithelial variety of mesothelioma, the most common and least aggressive form. WDPM is most often benign, but it can turn into malignant mesothelioma. Treatments vary and there is no routine strategy for it due to the rarity of this condition. It has most often been seen in the peritoneum of female patients, although there have been pleural and testicular forms of WDPM reported.

Facts about WDPM

Mesothelioma can be typed by location in the body. Most cases are diagnosed as pleural or as forming in the pleura around the lungs. The next most common form of the cancer attacks the peritoneum, the lining in the abdomen. Rarely, mesothelioma affects the pericardium around the heart of the tunica vaginalis of the testes. Most cases of WDPM have been peritoneal and in women. There have been reported cases of the other forms as well, but these are much rarer.

Only a few studies have investigated WDPM and these have looked at case studies, describing individuals diagnosed with the condition. WDPM is mostly benign and comes with a good prognosis and survival rates. However, it can turn malignant over time, which is why anyone diagnosed with WDPM needs to be careful and must be screened regularly for any malignancies.

Unlike malignant mesotheliomas, WDPM does not necessarily cause many symptoms. It can cause fluid to build up in the pleura or peritoneum, and this may cause swelling or pain. In the tunica vaginalis it may also cause swelling in the scrotum or the presence of lumps on the testicles. There is no standard treatment for WDPM because it is so uncommon.

Papillary Structures

The name of this condition, well-differentiated papillary mesothelioma, is descriptive of the tumor’s characteristics. Well-differentiated refers to the fact that the cells in this kind of tumor still resemble healthy cells. Poorly differentiated tumors are those that have cells that have changed and are easily distinguished from healthy cells. Well-differentiated tumor cells also grow less rapidly and spread less than those that are poorly differentiated.

The growth pattern of the cells in a WDPM tumor is described as papillary. This means that they grow into finger-like structures, called papillae. Each of them is lined with a layer of uniform, branching, or coarse mesothelium cells. These structures are only visible under a microscope, but to the naked eye they grow as white to gray nodules between one and three centimeters in diameter. There may be a single tumor or multiple smaller tumors.

Diagnosis of WDPM

WDPM is not always diagnosed right away because it does not necessarily cause symptoms, or symptoms that are severe enough to send someone to the doctor. However, if a patient complains of swelling in the abdomen or testes or of pain, a doctor will begin with a physical examination and then use imaging screens to see what is going on inside the body. An X-ray, CT scan or MRI is used to image the body and allows a doctor to see if there are tumors or abnormal tissues that may be tumors.

A biopsy is the next likely step. A thin needle is inserted where the imaging scan shows a potential tumor. The needle will remove a small sample of tissue and fluid to be examined by a pathologist. In cases in which the tumor is unreachable by a biopsy needle a patient may need to undergo a more invasive procedure to for a sample to be biopsied. Because there are not always symptoms with WDPM, it is sometimes diagnosed only after a patient has had surgery for another reason and the surgeon finds the tumor.

Pathologists look at biopsy samples under a microscope and examine the cells and the tumor’s structure to determine if it is benign or malignant, the type of cancer, and the subtype or cellular type. Sometimes the characteristic structures of WDPM can be seen in a CT scan, but the best way to diagnose it is with a biopsy. Malignant and aggressive types of mesothelioma may have papillary structures, so having a biopsy done to distinguish between these cancers and WDPM is important for informing treatment and giving a patient a prognosis.

Even with a biopsy it is possible to misdiagnose WDPM, especially since it is so rare. It may be mistaken for and adenomatoid tumor, tuberculosis peritonitis, different types of papillary carcinomas, peritoneal carcinomatosis, or reactive mesothelial hyperplasia. Checking for the presence of certain biomarkers in a biopsy sample is another way that a more accurate diagnosis may be made.

Treatment

Because WDPM is so rare there is no standard treatment plan for it. The treatment strategy will vary depending on the individual. Surgery may be done to remove a WDPM tumor, but some doctors feel this is too aggressive and risky a treatment strategy for a type of cancer that is not likely to be malignant. Others feel it is a reasonable strategy, especially if there are symptoms that might be relieved by reducing the size of the tumor.

Chemotherapy and radiation are other options, but results from these treatments have been mixed. In one study the patients that received both treatments died, but the researchers were uncertain if it was the therapy or the tumors that were the cause of death. There simply isn’t enough research to be sure what kinds of treatments will work for WDPM.

Prognosis

Also because the disease is rare, making a prognosis for WDPM is not easy. The cases that have been studied have resulted in varying survival rates, although generally the prognosis is better than for malignant types of mesothelioma. In one case study a woman lived 24 years after a diagnosis of WDPM. In another study of 24 patients with pleural WDPM, the survival times after diagnosis ranged from three years to 15 years. In a case study of WDPM of the tunica vaginalis, the man was healthy and tumor-free four years after being diagnosed.

Although WDPM is largely non-malignant, it can become malignant in some cases. It is important that whatever treatment or prognosis is given, that patients understand the risk and that the rarity of the condition means that definite answers cannot be given. Regular follow-ups and screenings is important in the event that the WDPM becomes malignant and starts to grow rapidly and spread.

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