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Standardizing Surgical Treatment in Malignant Pleural Mesothelioma

Malignant pleural mesothelioma (MPM) affects each individual uniquely, and due to the rarity of the disease, trending widespread results to treatment can be difficult. This is due to the fact that most of our knowledge of MPM results from retrospective studies performed by single-institutions and prospective phase I or II trials typically involve a small numbers of patients. In addition, staging of MPM can be difficult and in many cases inaccurate due to the parameters of current imaging technology.

When operating on any tumor the goal is always to remove as much of the tumor as possible, this is especially difficult because of the areas MPM manifests such as the lining of the lungs and other organs. In MPM, patients typically undergo either an extrapleural pneumonectomy (EPP) or a pleurectomy decortication (PD), and are then treated with radiation or chemotherapy or both directly after surgery in an attempt to kill off any remaining tumor cells.

In an attempt to standardize MPM treatment protocol, the International Mesothelioma Interest Group (IMIG) and the the International Association for the Study of Lung Cancer (IASLC) collaborated to address the deficiencies in the staging of MPM. With the goal of improving the staging system for MPM, the Mesothelioma Domain was established. The previous system for staging was based only on data collected involving surgically treated patients. The Mesothelioma Staging Project will include data from surgically and non-surgically treated patients.

Based on a multinational survey performed, the following terminology was recommended for the Mesothelioma Staging Project:

  • Extrapleural pneumonectomy (EPP): en bloc resection of the parietal and visceral pleura with the ipsilateral lung, pericardium, and diaphragm
  • Extended pleurectomy/decortication (EPD): parietal and visceral pleurectomy to remove all gross tumor with resection of the diaphragm and/or pericardium.
  • Pleurectomy/decortication (P/D): parietal and visceral pleurectomy to remove all gross tumor without diaphragm or pericardial resection.
  • Partial pleurectomy: partial removal of parietal and/ or visceral pleura for diagnostic or palliative purposes but leaving gross tumor behind.

The purpose of the IASLC making these recommendations is to set a framework for publications which will allow better understanding of procedural trends and to standardize surgical classifications of MPM, not to necessarily govern the language used by individual surgeons.

Another area needing further definition is macroscopic complete resection (MCR) which is the complete removal of a tumor. MCR is difficult in MPM due to the locale, and often trace amounts of the tumor are left behind after surgery. Determining the exact amount of residual tumor is difficult and not all surgeons agree that MCR is accomplished if any tumor is left behind, no matter how small. A scoring system for other malignancies has been developed based on the amount of tumorous tissue remaining and is referred to as the Completeness of Cytoreduction Score (CC score). A similar gaging system would be beneficial in regards to MPM as leftover tissue after surgery directly correlates to survival and continued treatment.

Additionally, lung cancer patients undergo lymph node sampling at the same time as the cytoreductive surgery to assess lymph node involvement. MPM involves the same lymph nodes affected in lung cancer, but also ones not typically affected in lung cancer. The Mesothelioma Domain of the IASLC Staging Committee is currently devising a lymph node map for MPM which will allow for a more detailed prognosis and accurate staging of the disease.

Our understanding of MPM continues to develop and research is becoming more prioritized as knowledge of the disease becomes more commonplace. Establishing a standardized approach to MPM will not only allow researchers to discover clearer parallels among studies, but also assist in developing a widespread protocol for diagnosis and treatment.