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.
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