A research team including scientists from Wake Forest Baptist Health in North Carolina, the University of Mississippi Medical Center, and Memorial Sloan Kettering Cancer Center in New York has developed the first two-tier grading system for malignant peritoneal mesothelioma, a rare form of a rare cancer.
An estimated 10 to 30 percent of the approximately 3,000 people in the US diagnosed with mesothelioma each year have the peritoneal form of the disease. Like the pleural or lung-related form, peritoneal mesothelioma grows quickly, is resistant to treatment, and is associated with past exposure to asbestos.
Grading Vs. Staging in Mesothelioma Treatment
Tumor grade is a measure of the likelihood that a mesothelioma tumor will grow and spread, based on certain cellular characteristics. It is determined by a pathologist who must examine the nuclei and the rate of mitosis in peritoneal mesothelioma cells under a microscope.
In contrast, tumor stage is a measure of the extent to which a mesothelioma tumor has already spread in the body.
Because malignant peritoneal mesothelioma is so rare, few medical centers have had a large enough cohort of patients to develop a simple, reliable grading system. The developers of the new system are an exception.
Using a grading system developed in 2011 for pleural mesothelioma as a guide, the team divided their peritoneal mesothelioma cases into two tiers based on cellular characteristics and survival times.
If the grading system can be verified by other cancer centers, the hope is that it will enable oncologists to offer their peritoneal mesothelioma patients a more reliable prognosis.
Tumor Grade and Mesothelioma Survival
The group focused on forty-six patients with the epithelioid form of malignant peritoneal mesothelioma (the most common form), who were diagnosed between 1984 and 2013. All patients in the study underwent a combination of cytoreductive surgery followed by a heated rinse of chemotherapy drugs in their abdomen. This treatment protocol, known as HIPEC, has become standard for peritoneal mesothelioma in the US.
The researchers stratified patients into low-grade and high-grade tiers and calculated mesothelioma survival times for each of the two tiers.
“The low-grade tier had a higher overall survival with a median of 11.9 years and 57% at 5 years when compared with the high-grade tier with a median of 3.3 years and 21% at 5 years,” the group reports in the American Journal of Surgical Pathology.
The 18 peritoneal mesothelioma patients in the lower tier also appeared to enjoy more time without progression of their disease (median of 4.7 years) when compared to the 28 patients in the high tier. For these patients, their peritoneal mesothelioma began growing again within a median of 1.9 years after treatment.
“Our study is first to specifically evaluate and correlate nuclear features and level of mitoses with overall survival in malignant peritoneal mesothelioma with epithelioid subtype,” concludes the report summary.
Reliable prognostic tools help in treatment planning and can help doctors develop more tailored therapies.
Valente, K, et al, “A Histomorphologic Grading System that Predicts Overall Survival in Diffuse Malignant Peritoneal Mesothelioma with Epithelioid Subtype”, September 2016, American Journal of Surgical Pathology, Volume 40, Issue 9, pp 1243-1248