This article is about tumors involving the pleura and malignant pleural mesothelioma. It will cover what the pleura is and possible treatment options for cancer involving the pleura with respect to anatomy of the pleura.
Each lobe of the lung is covered by a double layer sac called pleura. This covers the lung; it lines the chest wall, diaphragm and mediastinum (a membranous partition between the lungs). The layer that covers the lung is known as the visceral pleura, the layer that covers the chest wall is parietal pleura. Pleura also lines the diaphragm as well as the pericardium (the sac around the heart). The space between the two pleural layers is termed the pleural space.
There are approximately two to three thousand new cases of primary cancers of the pleura or malignant pleural mesothelioma that are diagnosed each year in the United States. It is known that exposure to asbestos is a risk factor for developing mesothelioma.
Tumors of the pleura can also be (and are more likely to be) secondary metastases from cancer involving distant parts of the body such as the colon, prostate and ovary. Primary pleural malignancies (and this is defined as tumors that arise from the pleura itself) are fairly uncommon. This is why physicians tend to have a difficult time making the initial diagnosis of mesothelioma.
Medical professionals continue to learn more about malignant pleural mesothelioma with respect to the diagnosis, management and possible treatment options. For a subgroup of patients multi-modality therapy or the combined use of chemotherapy, radiation and surgery is associated with better outcomes than the use of any single one of those treatment options alone.
Therefore survival of patients with mesothelioma is beginning to improve. Up to 80% of cases of mesothelioma are associated with asbestos exposure. The remaining cases can be related to family contact, as well as non asbestos type causes.
People most often are diagnosed with mesothelioma in their 50s to 70s and males are affected more often than females. It can be difficult to differentiate a malignant pleural mesothelioma from a different type of cancer that is referred to as metastatic adenocarcinoma (a malignant tumor formed from glandular structures in epithelial tissue). These are two completely different types of cancer with vastly different treatment options. Pleural tumors are more frequently metastatic cancers than mesothelioma and so doctors utilize many different tests to accurately make that distinction.
It is crucial to have enough tissue sample or a large enough biopsy specimen to adequately characterize not only the tumor as a mesothelioma, but also to distinguish which subtype of mesothelioma it is – epithelioid, sarcomatoid or mixed.
Epithelioid mesothelioma is the more favorable subtype of mesothelioma and carries a greater chance of survival after surgical and multi modality therapy.
Sarcomatoid mesothelioma is composed of spindle-shaped cells, and these tumors tend to have a less favorable outcome.
Part of the difficulty in making a diagnosis of mesothelioma are the subtle symptoms people exhibit. Dyspnea or difficulty with breathing is the most common symptom and that is usually due to the presence of a pleural effusion.
Pleural effusion is excess fluid that accumulates in the pleural cavity, the fluid-filled space that surrounds the lungs. This excess fluid can impair breathing by limiting the expansion of the lungs.
It accumulates in the spaces between the visceral pleura and the parietal pleura in between the lung and the chest wall.
Chest pain can also be common. Other symptoms include cough, loss of appetite, weight loss, night sweats and even hemoptysis or spitting up blood. On physical exam there may be decreased breath sounds on the affected side. There can also be a mass in the chest wall and this could be painful.
There are a number of Radiologic tests that may be used while trying to establish the diagnosis, the stage (which tells us how advanced the cancer may be) and determine if surgery is feasible and in the best interest of the patient.
- CT scans of the chest provide some very useful data
- PET scans help determine if there is any suggestion of disease in the other lung, in the abdomen, or in other areas of the body
- MRI can suggest invasion into the chest wall, mediastinum, or across the diaphragm into the abdomen (this usually indicates that surgery would not be an option that would benefit the patient)
All the information gathered including CT MRI PET as well as histology from the tissue biopsy is used to gain a better idea of the anatomy of one’s mesothelioma and whether surgery will be of potential benefit for the patient.
The first invasive test used in an attempt to make a diagnosis of mesothelioma is typically a thoracentesis. A thoracentesis is the use of a small catheter to drain pleural fluid that is sent for analysis to a pathologist to see if cancer cells are indeed present.
It is not uncommon that the pleural fluid is analyzed and does not indicate a diagnosis of mesothelioma or even cancer at all. Even if cancer is present in that space, oftentimes the next step is the use of a CT scan to guide a pleural biopsy.
A CT scan yields a diagnosis of mesothelioma approximately thirty to fifty percent of the time – better but still not great with respect to making a definitive diagnosis of mesothelioma. It can reveal the pleural abnormalities suggesting mesothelioma, but it does not give any definitive diagnosis. A biopsy is needed.
Lastly, an operation can be performed usually through a single small incision in the chest wall. A video scope is introduced into the pleural space and multiple biopsies are taken of the pleural surfaces. This is often a diagnostic intervention that results in a definitive diagnosis of malignant pleural mesothelioma. At this point the patient typically is referred to a thoracic surgeon with experience of treating patients with mesothelioma.
Doctors “stage” every patient with mesothelioma – in other words they determine how advanced they believe the cancer to be. When attempting to determine the best treatment option possible, doctors utilize all the data available to them including the CT, PET, CT MRI, tissue biopsy and eventually add a procedure in the operating room called a mediastinoscopy. This is a procedure where a small incision is made at the base of the neck and mediastinal lymph nodes are biopsied.
If the mediastinal nodes are negative for cancer – meaning no cancer is present – patients tend to live longer than if the nodes are involved with cancer. If the possibility of mesothelioma existing in the abdomen is suspected, a laparoscopy may be performed to assess this. This involves going to the operating room where a small incision and cameras are used to obtain tissue to determine whether mesothelioma is present in the in the abdomen.
Thoracic Surgery for Treating Mesothelioma
There are two operations that thoracic surgeons may consider performing for patients with mesothelioma. These are named pleurectomy/decortication (P/D) and orextrapleural pneumonectomy (EPP).
P/D is a surgical procedure that involves removing both the viscera and parietal pleura. This leaves the lung in place and can be a potential option for patients with very minimal or very advanced disease.
Orextrapleural Pneumonectomy (EPP)
EPP is the complete removal of the lung with its visceral pleura, the parietal pleura, the diaphragm and the sac around the heart (termed the pericardium). Both the pericardium and the diaphragm are then reconstructed using prosthetic material. Many surgeons regard EPP as the better choice for people who are strong, are younger or who have more bulky disease.
There is no “gold standard” therapy for mesothelioma. A person’s treatment plan depends on the anatomy of their tumor and their overall status. Sometimes patients with mesothelioma are treated with chemotherapy first followed by surgery and then radiation.
In certain cases, the “SMART” protocol of radiation first over five days, followed by surgery is being utilised. Patients may or may not need chemotherapy afterwards (depending on the pathology found at surgery). With this protocol, survival rates reported are dramatically better than published previously.
In the past mesothelioma was considered to be a disease that could not be treated, in which only pain management should be offered. Currently there are multiple interventions available that can help certain patients live longer and more comfortably. There has also been progress with regard to accurate diagnosis prior to surgery, which has been of great benefit.
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