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Mesothelial Hyperplasia and Proliferation

When cells of the mesothelium proliferate and grow more than normal, it can be difficult to determine if it is benign or malignant. It has always been a challenge for doctors to distinguish between mesothelioma and other types of cancer, making diagnosis difficult. But often overlooked is the issue of distinguishing between malignant mesothelioma and a benign proliferation of cells.

Known as reactive mesothelial hyperplasia or proliferation, this condition involves an unusual growth in the number of cells in the mesothelium. While it is not malignant, it may become cancerous later and can cause uncomfortable symptoms. An accurate diagnosis is important to treat either condition in a timely manner and to avoid a benign proliferation developing into a malignancy.

What is Mesothelial Hyperplasia?

Also known as mesothelial proliferation, hyperplasia is any increase in the number of cells in the mesothelium. An increase of cells in tissues that don’t normally grow and divide rapidly is not necessarily indication of cancer. There are other reasons, including simple irritation of the tissue that can cause cells to proliferate in a benign manner. Sometimes there is no explanation for why it occurs.

What Causes Benign Mesothelial Proliferation?

The reason for mesothelial cells proliferating in a way that is not malignant is not always known, but there are several potential triggers. It can be caused by an infection or may be a reaction to certain drugs. Hyperplasia may be a symptom of a collagen vascular disease or a result of surgery or a physical injury or trauma. A collapsed lung has also been known to be at the root of mesothelial proliferation.

Hyperplasia may also occur in the cells of the mesothelium in the abdomen, known as the peritoneum. This can be triggered by similar factors, like infection and inflammation, ovarian abscesses or an effusion or buildup of fluid in the peritoneum.

Diagnosing Mesothelial Hyperplasia

Hyperplasia can be detected by investigating biopsy samples under a microscope. Based on symptoms and imaging scans, a doctor may order a biopsy. This usually involves using a long, thin needle inserted into the chest cavity to remove a small piece of pleural tissue or into the abdomen for tissue from the peritoneum. A pathologist can look at that sample to determine if there is proliferation of the mesothelial cells.

Hyperplasia can be seen when the normally elongated mesothelial cells appear more cube-like in shape, but otherwise look normal. If those cells look unusual in anyway, like if they are abnormally large or are projecting into other areas of tissue, it may be considered a case of atypical mesothelial hyperplasia.

This does not automatically indicate that the proliferation is malignant, but it is possible and needs further tests to rule out mesothelioma. Ongoing diagnosis may involve blood tests to look for certain markers that can indicate cancer and ongoing testing of biopsy samples to look for abnormal or cancerous cells. Sometimes it is so difficult to tell if the proliferation is malignant, that a diagnosis of atypical mesothelial hyperplasia is given and doctors simply wait and continue to test a patient, looking for clear signs of malignancy.

Invasion Helps Distinguish Malignancy from Hyperplasia

While pathologists still find it challenging to determine if a proliferation of mesothelial cells is benign or malignant, recent research has found that invasion of the cells is a key factor that can be used to distinguish them. When the hyperplasia is seen in biopsy samples to be invading other tissues, this is a strong indication that the growth is malignant.

Specifically in the case of the mesothelium, when the cells invade fat tissue near the pleura it is more likely to be mesothelioma than benign hyperplasia. The cells may also invade lung tissue, muscle tissue, or the tissue of any other organ to be considered malignant, but fat is most commonly invaded.

Treating Mesothelial Hyperplasia

If doctors are confident diagnosing a mesothelial proliferation as benign there may be no treatment needed. Treatment should address the underlying condition causing the proliferation, but this cannot always be determined. An infection or injury that has caused the growth of cells can be treated, hopefully resulting in the reduction in the proliferation. If there is no cause that can be determined, treatment only proceeds if the growth is causing discomfort. Surgery is risky and is usually only done if the growth can be easily removed and will provide relief for the patient.

Another important consideration is the fact that the diagnosis could be incorrect. With so much difficulty in distinguishing between benign and malignant growths, even experts can make mistakes. Patients should feel empowered to request ongoing screenings to check the progress of the proliferation. Regular screenings can help track the growth and catch any signs of malignancy as early as possible.

Page edited by Dave Foster

Dave has been a mesothelioma Patient Advocate for over 10 years. He consistently attends all major national and international mesothelioma meetings. In doing so, he is able to stay on top of the latest treatments, clinical trials, and research results. He also personally meets with mesothelioma patients and their families and connects them with the best medical specialists and legal representatives available.

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