Small Cell Mesothelioma

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.

Cellular makeup of a small cell tumor

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.

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Growth Patterns

These cells are uniform in appearance. They are round and feature a single-bland nuclei that takes up the majority of the cell.

Small Cell Mesothelioma Cells

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.

Diagnosis and Treatment

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.

Illnesses that often resemble small cell mesothelioma:

  • Metastatic small cell carcinoma
  • Desmoplastic small round cell tumor
  • Primitive neuroectodermal tumor
  • Lymphoma

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.

Additional Resources

  1. Cavazza, A, et al. Small cell mesothelioma of the pleura: description of a case. Pathologica.(October 2002). Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/12417972
  2. O'Byrne, K, and Rusch, V. Malignant Pleural Mesothelioma. (2006). New York: Oxford University Press.
  3. Mayall, FG and Gibbs, AR. The histology and immunohistochemistry of small cell mesothelioma. (January 1992). Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/1310669
  4. Chahinian, A. (2002). Treatment of Malignant Mesothelioma: Radiotherapy and Chemotherapy. In B. Robinson & A. Chahinian (Eds.), Mesothelioma (pp. 185-199). London: Martin Dunitz.
  5. Hammar, S. Macroscopic, histologic, histochemical, immunohistochemical and ultrastructural features of mesothelioma. (27 February 2005). Retrieved from http://www.ultrapath.org/
  6. Allen, T. Recognition of Histopathologic patterns of diffuse malignant mesothelioma in differential diagnosis of pleural biopsies. Archives of Pathological Laboratory Medicine. (November 2005). Retrieved from http://www.archivesofpathology.org/doi/pdf/10.1043/1543-2165%282005%29129%5B1415%3AROHPOD%5D2.0.CO%3B2
  7. Ordonez, NG. Mesotheliomas with small cell features: Report of eight cases. Modern Pathology. (25 May 2012). Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/22222641

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