Revisions to a leading pleural mesothelioma staging system are in order, according to a collaborative study between the International Mesothelioma Interest Group (IMIG) and the International Association for the Study of Lung Cancer (IASLC).
In 1995, with hopes of improving the poor survival rates of malignant mesothelioma patients, the International Mesothelioma Interest Group built upon previous methodologies to develop the IMIG staging system.
Oncologists evaluate a patient’s tumor characteristics using a cancer-specific TNM System. A crucial aspect of the IMIG system, TNM describes a tumor’s size (T), lymph node involvement (N) and metastasis (M), or spread to distant sites.
Doctors use these descriptors to assign a stage to a patient’s cancer. The stage reflects the extent or severity of cancer, which can affect the course of treatment and the patient’s prognosis.
After nearly two decades, the IMIG system remains one of the most widely used mesothelioma staging systems to date. But concerns over the system’s validity prompted an international panel of mesothelioma experts to investigate potential areas for improvement.
With a more effective staging system in place, doctors will be one step closer to providing patients with the most appropriate mesothelioma treatments. They can also better define groups of patients with a similar outlook, which is invaluable for accurately grouping and analyzing data collected in clinical trials.
Issues with the IMIG System
Led by Dr. Valerie Rusch, chair of the IASLC’s mesothelioma subcommittee and thoracic surgeon at the Memorial Sloan-Kettering Cancer Center, the study identified several weaknesses of the IMIG staging system to be addressed in future studies.
The study’s co-authors include world-renowned mesothelioma specialist Dr. Harvey Pass, Director of Thoracic Surgery at the NYU Medical Center, as well as seven other IASLC members from six nations.
A leading concern of the researchers was that IMIG developed the system using a small series of retrospective surgeries. This makes it difficult to assign an accurate cancer stage based solely on a patient’s clinical information.
Additionally, the IMIG system classifies the cancer’s lymph node involvement with descriptors borrowed from the International Lung Cancer Staging System, which may not be relevant to pleural mesothelioma. The researchers also suggest revisions to staging groups, especially Stages I and II.
While Rusch and colleagues confirmed that the IMIG system can accurately distinguish between key categories of mesothelioma tumor progression and lymph node involvement, they found the system’s shortcomings hindered progress in our understanding of the disease.
Other Findings and Future Research
In the study, which will appear in the November 2012 issue of the IASLC’s Journal of Thoracic Oncology, researchers analyzed 3,101 mesothelioma patients from 15 cancer centers. The data set includes patients from four continents.
Among several red flags identified, researchers confirmed their suspicion that current data largely represents mesothelioma patients treated with surgery, an unlikely option for patients with advanced stage disease.
Stage classifications for this group of patients might also need to be reassessed. In the future, researchers say, “the addition of a larger group of patients with more advanced disease, staged clinically and managed non-surgically, may help determine whether Stages III and IV should be classified into a and b categories.”
They also report that the system’s tumor (T) descriptors are based on qualities that can be observed but not measured. This makes the descriptors most applicable to staging that depends on biopsy results as opposed to clinical data. The authors suggest that T descriptors could be enhanced with precise measurements of tumor volume.
Lastly, researchers were concerned about an unclear distinction between N1 and N2 disease, which describe the extent of the cancer’s spread to the lymph nodes. The data clearly reflects improved survival for patients with no lymph node involvement, but further research on N classifications may yield noteworthy improvements to the IMIG staging system.
An improved, universally-accepted staging system for pleural mesothelioma will lead to more accurate predictions of patient outcomes. Further, it will allow researchers to develop a deeper understanding of the cancer’s behavior.
To guide future research and improvements to the system, IMIG and the IASLC created a large international database of malignant pleural mesothelioma patients.