Well-Differentiated Papillary Mesothelioma
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Well-differentiated papillary mesothelioma, or WDPM, is a rare epithelioid mesothelioma subtype. WDPM is usually benign but can turn into malignant mesothelioma. It is most often seen in the peritoneum of female patients, although there have been reported pleural and testicular forms of WDPM.
Facts about WDPM
Mesothelioma is primarily dentified by its location in the body. Most cases are diagnosed as pleural, meaning they formed in the pleura around the lungs. The next most common form attacks the peritoneum, the lining in the abdomen. Rarely, mesothelioma affects the pericardium around the heart or the tunica vaginalis of the testes.
Cell type, like well-differentiated papillary, is another way to identify different types of this cancer:
- Most cases of WDPM have been peritoneal and in women.[1] There have been reported cases of the other forms as well; although, these are even rarer.
- Relatively few studies have focused on WDPM. These have examined 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. Therefore, anyone diagnosed with WDPM should receive regular screening for malignancies.[2]
- 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.
- In the tunica vaginalis, it may also cause swelling in the scrotum or 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 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.[2] 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.
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 if the sample is 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.
Even with a biopsy, it is possible to misdiagnose WDPM. WDPM 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.[3]
Treatment
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 are other treatment options. However, the disease may recur after some time. In one study, a patient who received both treatments had a 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.[4]
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.[2]
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.[6]
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.
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Dr. Pinar Kanlikilicer has a PhD in Biomedical Engineering. She completed her 5-years of postdoctoral training in the Department of Experimental Therapeutics at MD Anderson Cancer Center. She is currently working in the field of cancer as a research scientist.