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Where Does Papillary Mesothelioma Develop?

The majority of well-differentiated papillary mesothelioma tumors develop in women, specifically in the abdominal cavity. Less commonly, doctors have found WDPM tumor growth on several of the body’s protective membranes, including the pleura (lining of the lungs), pericardium (heart sac) and tunica vaginalis (lining of the testes).

Is WDPM Cancerous?

From a medical standpoint, these tumors are practically benign. Studies have reported WDPM turning into malignant mesothelioma over time, although the chance of this happening is unlikely. Some people with WDPM have also experienced multiple recurrences after treatment.

A February 2019 study published in the Annals of Diagnostic Pathology observed 75 cases of WDPM diagnosed between 2000 and 2017 at Fudan University Shanghai Cancer Center in China.

Patients in the study included 58 females and 17 males ranging in age from 18 to 69 years. Of the 75 cases, only one turned cancerous.

A 2021 research report in Modern Pathology stated that solid papillary mesothelioma tumors appear to be either benign or very low-grade tumors that need to be separated from malignant mesotheliomas.

Is There an Asbestos Connection?

At this point, researchers are unsure whether papillary mesothelioma is linked to asbestos exposure. Some patients have a history of asbestos exposure, but most do not. The cause of this disease remains poorly understood.

According to a 2019 study published in Annals of Surgical Oncology, approximately 50 cases of WDPM in the peritoneum have been described in medical literature. There are also several small case reports of WDPM of the pleura. Another study indicated that there are fewer than 20 documented cases of testicular papillary mesothelioma.

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Symptoms and Characteristics

well-differentiated papillary mesothelioma
Pathology examination of well-differentiated papillary mesothelioma.

Many cases of well-differentiated papillary mesothelioma have no symptoms, but the disease has been known to cause pain and excessive fluid buildup in the pleura or abdomen of some patients.

WDPM of the tunica vaginalis can cause scrotal swelling or the formation of testicular lumps. In one study of 22 WDPM cases, only two patients reported to their doctors with symptoms. One patient experienced acute abdominal pain, and the other had chronic pelvic pain.

Primary Characteristics of WDPM

  • 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 tumor’s cells feature 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.
  • Papillae sometimes create round swirls of calcium known as psammoma bodies.
  • Tumors form white or grey nodules ranging from less than 1 centimeter in size to more than 3 centimeters.
  • WDPM can develop as a solitary mass or arise in many sites. The latter is known for more aggressive behavior.
  • Tumors are smaller than 1 centimeter in more than half of all cases.

Misdiagnosis and Challenges

Because well-differentiated papillary mesothelioma rarely causes symptoms, doctors usually discover tumor growth during an unrelated pelvic or abdominal surgery. WDPM can sometimes be found with an imaging test, such as 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 a 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.

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

Papillary Mesothelioma Treatment

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 a combination of the main types of mesothelioma treatment, including surgery, chemotherapy and radiation therapy.

Treatment options also depend on where the papillary mesothelioma tumors form.

For example, WDPM on the peritoneum may be treated with a combination of cytoreductive surgery and hyperthermic intraperitoneal chemotherapy, also known as HIPEC. In the 2019 study published in Annals of Surgical Oncology, 37 of the 56 patients were treated with this combination.

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    Prognosis and Survival Rate of Papillary Mesothelioma

    The survival outlook for patients with well-differentiated papillary mesothelioma is significantly better than the prognosis of patients with most other mesothelioma cell types.

    While only 5% to 10% of malignant mesothelioma patients survive five years after diagnosis, several patients with WDPM have survived for decades.

    Median Survival for Well-Differentiated Papillary Mesothelioma
    WDPM of the Pleura WDPM of the Peritoneum
    6 years and 2 months 12 years
    Source: American Journal of Surgical Pathology, 2004; Annals of Surgical Oncology, January 2019

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