Small cell mesothelioma is an extremely rare subtype of the cancer. As the name suggests, cancerous cells in these tumors are smaller than cells in other forms of the disease.
It is most commonly classified as a subtype of the epithelial cell type, but in one study of eight mesotheliomas with small cell features, only four were epithelial. The other four were biphasic, indicating a combination of both epithelial and sarcomatoid cells.
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Small cell mesothelioma is much less common than other forms, such as adenomatoid or tubulopapillary. Less than 6 percent of all mesothelioma tumors have a small cell pattern.
Most of these tumors are not made up entirely of small cells. Instead, they often also contain normal mesothelioma cells and other assorted neoplastic cells. Roughly half of all cells in the tumor should display a small cell pattern for the tumor to qualify as this type.
These cells are uniform in appearance. They are round and feature a single-bland nuclei that takes up the majority of the cell.
This type of mesothelioma grows in a pattern that is similar to small cell carcinoma, but the mesothelioma tumors do not display the stream, ribbon or rosette patterns that appear in the carcinoma. These tumors most commonly grow in the peritoneum, although they can also arise in the pleura or the pericardium.
It can be challenging to correctly diagnose this cell type. The cells can look very similar to other small cell neoplasms, and doctors must run immunohistochemical tests to differentiate between the diseases.
A single biopsy specimen may not always contain an accurate ratio of these cells. In one study, small cells made up 80 to 100 percent of the biopsy material, but only 15 to 20 percent of the full tumor. As a result, doctors may need to retrieve several samples to make an accurate diagnosis.
Once the samples undergo immunohistochemical staining, the different types of cells in the tumor all test positive for different compounds. Malignant small cell mesothelioma tests negative for several neuroendocrine markers, such as CD56 and chromogranin.
Although there are too few cases of small cell mesothelioma to have a detailed standard of treatment, most doctors approach it the way they would approach any other type of the cancer. In a 2012 study of eight small cell mesothelioma patients, six patients passed away during the observation period. The mean survival time of these patients was 8.2 months.
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