Benign Mesothelioma

Benign mesothelioma is a highly treatable, non-cancerous form of mesothelioma with a recurrence rate of only about 10%.

Key Points

  • 1

    Benign mesothelioma is extremely rare and has four main types.

  • 2

    The cause of benign mesothelioma is unknown and it can occur at any age.

  • 3

    This type is usually treated with curative surgery, which has a high success rate.

  • 4

    Though usually easily treated, in some cases benign tumors may become malignant.

A non-cancerous, very rare form of mesothelioma, benign mesothelioma often only requires one surgery to completely and successfully remove the tumor. There are a number of different types of benign mesothelioma, all of which have different characteristics, features, and behaviors than malignant mesothelioma.

Benign Mesotheliomas Differ From Malignant Mesotheliomas

Mesothelioma can generally be classified as benign or malignant. While malignant mesothelioma has a 20-50 year latency period, benign mesothelioma can be diagnosed at any age. While symptoms can be similar between the two types, benign tumors usually do not invade surrounding tissue or organs, nor do they spread to other parts of the body (metastasis).

By contrast, malignant tumors usually demonstrate more aggressive growth, tissue invasion, and spread. In terms of a cause, the majority of patients with malignant mesothelioma have a history of asbestos exposure. Benign mesothelioma, however, is not the result of asbestos exposure, and the exact cause remains unknown. Benign mesothelioma, unlike its malignant form, is relatively easily treatable and has a low mortality rate.

Sometimes, a mesothelioma may appear benign but recur, spread locally, or become malignant. If diagnosed with benign mesothelioma, successfully treated patients will likely still need follow-ups to monitor for new tumor growth.

Benign MesotheliomaMalignant Mesothelioma
CauseUnknownAsbestos Exposure
Latency PeriodOccurs at any age20-50 years
Mortality RateLowHigh
TreatmentOften successful with one surgeryOften palliative, depending on tumor and patient factors
MetastasisTumors don’t spread, but can grow in size or recurCan spread to other organs and lymph nodes

Diagnosing Benign Mesothelioma

Most of the time, diagnosis of benign mesothelioma is accidental. In other words, the tumor is discovered during tests for unrelated purposes. Accurate diagnosis for benign mesothelioma mirrors the process for malignant mesothelioma and includes:

  • Complete medical history
  • Physical exams
  • Imaging tests such as X-rays, CT scans, and MRI scans
  • Tissue or fluid biopsy
  • A biopsy is the recommended way to definitively diagnose a benign mesothelioma.

There Are Four Types of Benign Mesotheliomas

There are four main types of benign mesotheliomas, and the characteristics of each differ based on location and cell structure. All types are relatively easy to treat and have good prognoses. While the most common form of malignant mesothelioma is pleural mesothelioma, where the tumors develop in the lining of the lungs, benign mesotheliomas most often occur in the peritoneum, or lining of the stomach.

Benign Multicystic Peritoneal Mesothelioma (BMPM)

This is a very rare tumor and as the name indicates, it contains numerous cysts and originates in the abdominal cavity, most often in the pelvis specifically.

  • More than 75% of cases occur in women of childbearing age.
  • It can resemble other cystic abdominal disorders.
  • The symptoms are vague and include chronic or intermittent abdominal or pelvic pain and abdominal distention.
    Diagnosis usually relies on tissue biopsy.
  • Treatment is surgery to remove the entire tumor mass and surrounding tissue. Neither chemotherapy nor radiation is indicated in usual circumstances.
  • Local recurrence rates vary with most in the 25% to 50% range.

Recurrence usually requires repeat surgery, although some success in female patients using anti-estrogen therapy has been reported. A normal lifespan is likely, even with benign recurrences. Very rarely, these tumors can evolve into an aggressive, malignant form. This, and the risk of benign tumor recurrence, makes long term monitoring important.

Well-Differentiated Papillary Mesothelioma (WDPM)

As a well-differentiated tumor, WDPM is a type of mesothelioma that more closely resembles its normal cell-of-origin, characteristically does not invade underlying normal tissue, and grows more slowly than its malignant epithelioid counterpart. While it’s usually benign, there have been cases of malignant cells found with benign cells.

  • WDPM occurs more frequently in the abdomen of females of reproductive age.
  • Asbestos exposure is identified in only about half of the cases.
  • Symptoms include breathing difficulty or cough, and effusions.
  • It may also occur in the pericardium, pleura, and testicular lining.

ŸFor many patients, the diagnosis is made after incidentally discovering a mass on chest x-ray or other radiologic imaging, or at the time of surgery for unrelated conditions. It may also be identified during an evaluation of a pleural effusion on one side of the chest.

ŸWhen there is little to no tumor progression, some patients have elected close monitoring in lieu of immediate treatment, thus avoiding any serious consequences of therapy.  However, based on its epithelioid mesangioma origin, and its variable prognosis, many feel that treatment is a reasonable option.

The types of reported treatments for WDPM include surgery, chemotherapy given systemically or directly into the chest, and radiation therapy.  Given the scarce information about WDPM treatment, therapy is tailored to the location, progression, and extent of the tumor, as well as the clinical condition of the patient.

ŸSome patients will have local tumor or pleural effusion recurrence, and it may develop into a malignant form of mesothelioma. In fact, this type carries the greatest risk of becoming malignant.

Benign Adenomatoid Tumor (AT)

These are slow growing tumors that often cause no symptoms. Some patients with a pleural benign adenomatoid tumor, however, can experience localized chest pain. Most benign adenomatoid tumors are discovered incidentally on radiologic imaging or at the time of surgery for unrelated conditions. However, in males they also are identified when evaluating a scrotal mass.

  • These benign tumors often originate within the reproductive organs in males and females.
  • They rarely become malignant.
  • Most are small with clearly delineated margins.
  • ŸThey do not recur following complete surgical resection.
  • No chemotherapy or radiation treatments are indicated.

ŸAlthough benign, adenomatoid tumor cells have identifying markers similar to normal mesothelial and mesothelioma cells. Adenomatoid characteristics can often be found in malignant mesothelioma tumors of the epithelioid type.

ŸIn the chest, imaging or direct (surgical) assessment can also assist in differentiating benign adenomatoid tumors from malignant adenomatoid mesothelioma. The presence of diffuse thickening and inflammation of the pleural membranes, multiple tumor nodules, or a significant pleural effusion is strongly indicative of malignancy.

Localized Fibrous Tumor of the Pleura (LFTP)

This tumor was previously referred to as “benign” or “localized” mesothelioma, but its cellular origin is different from mesothelial cells. Between 70% and 90% of LFTP are benign and the remaining cases are malignant. A small proportion of the benign form also may become malignant and recur. Because of its pleural location, malignant mesothelioma is also considered in the evaluation.

  • ŸThe median age at the time of diagnosis is 55 to 60
  • The tumor occurs in men and women equally.
  • Symptoms are rare, but may include chest pain, cough, and low blood sugar
  • Diagnosis usually requires a biopsy

ŸBecause tumor recurrence and malignant transformation occur, complete surgical resection is the treatment of choice. Neither chemotherapy nor radiation treatment are considered to have a role in the treatment of benign LFTP.

The survival Ÿoutcome of benign LFTP is very good following successful surgical resection. One report showed no recurrence after surgical resection in 100% of benign tumors.

Treatment Is Usually Successful

Overall, treating benign mesothelioma is relatively simple and carries a high success rate. Curative surgery that resects the entire tumor is important to reduce the risk of developing a malignancy. Despite treatment, there have been cases of recurrence, and some tumors still become cancerous. Continuous monitoring is crucial following a successful surgery to reduce the risk of developing late stage disease.

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