Well-differentiated papillary mesothelioma is a rare type of mesothelioma that most often occurs as peritoneal mesothelioma in women. WDPM is usually benign but can turn into malignant mesothelioma. There have been a few reported cases of pleural and testicular forms of WDPM.
Facts About Well-Differentiated Papillary Mesothelioma
Mesothelioma is primarily identified by its location in the body. Most cases are diagnosed as pleural, meaning they form in the pleura around the lungs. The next most common form attacks the peritoneum, the lining of the abdomen. Rarely, mesothelioma affects the pericardium around the heart or the tunica vaginalis of the testes.
Mesothelioma is also categorized by broad cell types. Epithelial is the most common form, and sarcomatoid is the rarest. Biphasic is a mixture of these two cell types.
Experts further divide these cell types into subtypes, many of which are rare. One of these is well-differentiated papillary. Because it is rare, only a few facts are known about well-differentiated papillary mesothelioma (WDPM):
- Most cases of WDPM have been peritoneal and in women.[1]
- Most of the few studies of well-differentiated papillary mesothelioma are case studies of individuals with the diagnosis.
- A review of 26 case studies included a wide age range of women with peritoneal WDPM, from 23 to 75.[2]
- WDPM is mostly benign and comes with a good prognosis and survival rates.
- The benign form can turn malignant over time. Therefore, anyone diagnosed with WDPM should receive regular screening for malignancies.[3]
- Unlike malignant mesotheliomas, WDPM does not typically cause many symptoms. The disease can cause fluid build-up in the pleura or peritoneum, which in turn can result in swelling or pain.
Cell and Tumor Characteristics
The name of this condition, well-differentiated papillary mesothelioma, is descriptive of its tumor characteristics. Well-differentiated refers to the fact that cells in this kind of tumor resemble healthy cells.
Poorly differentiated tumors have cells that 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 papillary. This means they grow into finger-like structures called papillae.[4] Each structure is lined with a layer of uniform, branching, or coarse mesothelium cells. These structures are only visible under a microscope.
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.
Is Well-Differentiated Papillary Mesothelioma Always Benign?
Well-differentiated papillary mesothelioma is almost always benign. It is possible that it can become malignant over time, but this isn’t common.
The incidence of WDPM turning malignant may be overestimated because of misdiagnosis. Some patients may be diagnosed with WDPM when what they actually have is malignant mesothelioma.
Does Asbestos Cause Well-Differentiated Papillary Mesothelioma?
In the review of 26 case studies of women with the peritoneal form, none had any known asbestos exposure.[2]
In a different review of 14 cases of WDPM, six had a history of asbestos exposure, but this study included men. Men have a higher risk of exposure because of workplace use of asbestos.[1]
The connection between WDPM and asbestos is much less certain than with other types of mesothelioma. Because it is so rare, no one currently has a good understanding of what causes it.
One case study of a woman with WDPM found that it arose from endometriosis, a condition in which tissue similar to the lining of the uterus grows outside the uterus. She was also diagnosed with endometrioid adenocarcinoma.[5]
Symptoms of Well-Differentiated Papillary Mesothelioma
Most people with this diagnosis have minimal or no symptoms. Among women with the peritoneal form, some have abdominal pain and swelling. Many don’t discover they have the disease until undergoing surgery for another condition.
The very rare cases of pleural or testicular WDPM may cause symptoms, but evidence is lacking. The testicular form seems to cause pain, lumps, and swelling.
Diagnosis of WDPM
WDPM is not always immediately diagnosed because it does not often present symptoms severe enough to send someone to the doctor.
However, if a patient complains of swelling or pain in the abdomen or testes, a doctor will begin with a physical examination. Next, an X-ray, CT scan, or MRI will image the body, allowing a doctor to see any tumors or abnormal tissues.
A biopsy is the next likely step. A doctor inserts a thin needle where the imaging scan shows a potential tumor. The needle removes a small amount of tissue or a fluid sample to be examined by a pathologist.
In cases where the doctor cannot reach the tumor, a patient may need to undergo a more invasive procedure to obtain a biopsy sample. Because WDPM does not always present symptoms, the condition is often only diagnosed after a patient has had surgery for another reason and a tumor is discovered.
Sometimes, characteristic structures of WDPM can be seen in a CT scan; however, the best way to diagnose it is with a biopsy. Pathologists examine biopsy samples under a microscope to determine whether they are benign or malignant.
In addition, the pathologist can collect information to identify the type of cancer and its cellular type. Since malignant and aggressive types of mesothelioma may have papillary structures, a biopsy to distinguish between these cancers and WDPM is important for informing treatment.
Diagnostic Challenges and Misdiagnosis
Even with a biopsy, WDPM can be misdiagnosed. It may be mistaken for an adenomatoid tumor, tuberculosis peritonitis, different types of papillary carcinomas, peritoneal carcinomatosis, or reactive mesothelial hyperplasia.
Checking for certain biomarkers in a biopsy sample is another way to make a more accurate diagnosis. Since genetic alterations also drive malignancies in many cancers, checking for a cancer-specific mutation may also help make the right diagnosis.
A recent study that included genome-wide sequencing analyses of WDPM tumors showed that all tumors harbored somatic mutations in either the TRAF7 or CDC42 genes.[6]
Another recent study found that malignant papillary mesothelioma can mimic the cell structure of true WDPMT. This makes it even more important to get an accurate diagnosis so that patients can get appropriate treatment.
The researchers also found that BAP1 mutations were important markers for distinguishing true WDPM from mesothelioma and should be used when doctors suspect a patient has WDPM.[7]
Treatments for Well-Differentiated Papillary Mesothelioma
Because WDPM is so rare, there is no standard treatment plan. The treatment strategy will vary individually. Surgery may remove a WDPM tumor, although some doctors feel this is an overly aggressive treatment strategy for a typically benign cancer.
Chemotherapy and radiation therapy are other treatment options. However, the disease may recur after some time. In one study, a patient who received both treatments had metastasis thirteen years after his treatment. This study highlights the malignant potential of WDPM.
In addition, WDPM patients may benefit from cytoreductive surgery (CRS) with hyperthermic intraperitoneal chemotherapy (HIPEC). One study suggests that cytoreduction and HIPEC treatment is more effective than debulking surgery in terms of disease recurrence or progression.[8]
What Is the Prognosis?
Determining a prognosis for WDPM is difficult because it is such a rare disease. Cases that have been studied resulted in varying survival rates, although, generally, the prognosis is better than for malignant mesothelioma. In one case study, a woman lived twenty-four years after diagnosis.[3]
In another study of twenty-four patients with pleural WDPM, survival times ranged from three to fifteen years.[5] In a case study of WDPM of the tunica vaginalis, the man was healthy and tumor-free three years after diagnosis.[9]
Although WDPM is largely non-malignant, it can become malignant in some cases. Patients must understand that the rarity of the condition means definite answers are virtually impossible. Regular follow-up exams and screenings are essential to ensure WDPM does not become malignant.
