S-100

S-100 is a family of proteins detected by immunohistochemistry staining of tissue samples. Certain tumors like melanoma and nerve sheath tumors stain strongly positive for S-100, while mesothelioma typically does not. Pathologists use S-100 along with other markers to distinguish mesothelioma from look-alike cancers.

Origin

S-100 was first isolated from cow brain tissue in 1965 by biochemists Blake Moore and colleagues. The name comes from the protein's solubility in 100%-saturated ammonium sulfate solution. The 'S' stands for 'soluble.' It has since been recognized as a large family of related calcium-binding proteins used widely in diagnostic pathology.

Significance in Asbestos Context

When a biopsy shows a tumor in the chest or abdominal lining, the pathologist must distinguish mesothelioma from other cancers that can look similar under the microscope, such as melanoma that has spread to the pleura, or rare nerve sheath tumors. S-100 is one of the 'negative markers' for mesothelioma, meaning mesothelioma is usually S-100 negative, while metastatic melanoma is strongly S-100 positive. A correct diagnosis matters enormously for asbestos claims, because compensation depends on confirming that the tumor is truly mesothelioma and not another cancer that mimics it. If your pathology report mentions S-100, it usually means the pathologist was carefully ruling out look-alike tumors before settling on a mesothelioma diagnosis.

Example Sentence

The immunohistochemistry panel showed the tumor was calretinin and WT-1 positive but S-100 negative, supporting a diagnosis of epithelioid mesothelioma rather than metastatic melanoma.

Related Terms

Immunohistochemistry, Calretinin, WT-1, Epithelioid Mesothelioma, Differential Diagnosis, Melanoma

Notes

• Ask your pathologist or oncologist for a copy of the full IHC panel used to confirm your diagnosis. S-100 status is often listed alongside calretinin, WT-1, CK5/6, and other markers.
• If S-100 was not tested and the diagnosis is uncertain, request a second-opinion pathology review at a mesothelioma specialty center (such as a National Cancer Institute–designated center).
• Preserve all pathology reports and the original biopsy slides or paraffin blocks; these may need to be re-examined by experts retained for a legal claim.
• A clear, well-documented IHC workup helps both your medical team plan treatment and your legal team establish the diagnosis required for compensation.