Patients who are diagnosed with sarcomatoid mesothelioma face a much poorer outlook than those with the more common epithelioid form of the disease, according to a study published online January 15 in the journal, Modern Pathology. The study also found evidence linking sarcomatoid mesothelioma with higher asbestos exposures, and confirmed that proteins called cytokeratins (CK) are among the most useful markers for diagnosing this type of mesothelioma.
Sarcomatoid mesothelioma is the least common form of this already rare cancer, comprising only about 10 percent of the 2,000 to 3,000 mesothelioma cases diagnosed in the U.S. each year. It is also the most aggressive type of this disease. Studies find that patients with sarcomatoid mesothelioma survive for an average of just five to six months.
That short survival time makes it essential for doctors to diagnose sarcomatoid mesothelioma as quickly as possible. “Accurate diagnosis of mesothelioma is important both for optimal treatment and determining progress,” says study author Victor L. Roggli, MD, Professor of Pathology at Duke University Medical Center. Yet sarcomatoid mesothelioma is among the most difficult forms of the disease to diagnose with any accuracy, because it can look very similar to other non-cancerous and cancerous tumors, including other sarcomas (a cancer that forms in connective tissue). “Some sarcomas that sarcomatoid mesothelioma can be confused with do better in terms of survival,” Dr. Roggli says.
The researchers say that immunohistochemistry—a diagnostic staining technique that looks for protein markers in cells that are specific to certain cancers—is not as useful for sarcomatoid tumors as it is for other types of mesothelioma. “Special stains are of rather limited benefit and if the pathologist relies on staining of the tumor alone, mistakes can be made,” Dr. Roggli says. However, of the immunohistochemical markers available, CK is among the most useful for diagnosing sarcomatoid mesothelioma. “The best approach to diagnosis is close communication between the radiologist looking at the films, the doctor who takes the biopsies (surgeon, radiologist, or pulmonologist), and the pathologist,” he says.
To learn more about this aggressive cancer, Dr. Roggli and his colleagues examined database records taken from 326 patients. They discovered that most of the patients with sarcomatoid mesothelioma had cancer in the chest area (pleura).
Using x-ray analysis, the authors found that patients had more asbestos fibers in their tissue samples compared with patients who had non-sarcomatoid tumors. “Our findings indicate that on average, sarcomatoid mesotheliomas are associated with heavier exposures to asbestos than the other mesothelioma types,” Dr. Roggli says. Most of those fibers were the amosite form of asbestos.
The researchers also confirmed that sarcomatoid mesotheliomas have a particularly dire prognosis compared with other forms of this cancer. In the study, only 30 percent of patients with sarcomatoid mesothelioma were alive at six months, and only 10 percent were alive after a year. By comparison, survival rates for the more common epithelioid mesothelioma are in the range of 12 to 24 months.
“Our study is the largest by far of this relatively rare form of a rare cancer (mesothelioma),” says Dr. Roggli. “Our findings confirm reports by others that this type has a rather grim prognosis, a strong association with asbestos, and location mainly in the chest.”
Klebe S, Brownlee NA, Mahar A, Burchette JL, Sporn TA, Vollmer RT, Roggli VL. Sarcomatoid mesothelioma: a clinical-pathologic correlation of 326 cases. Modern Pathology; 2010 Jan 15 [Epub ahead of print].
American Cancer Society. What are the Key Statistics About Malignant Mesothelioma?