MTAP

MTAP (methylthioadenosine phosphorylase) is a gene and its protein, normally present in most cells. In many mesotheliomas the MTAP gene is deleted along with the neighboring tumor-suppressor gene CDKN2A. Pathologists use loss of the MTAP protein, seen on an immunohistochemical stain, as a practical signal that this deletion has occurred, which helps confirm cancer.

Origin

The MTAP gene was characterized in the 1990s in studies of the 9p21 chromosome region. Its role as a stain-based surrogate for CDKN2A deletion in separating mesothelioma from benign tissue was established in pathology research during the 2010s.

Significance in Asbestos Context

One of the hardest problems in diagnosing mesothelioma is telling malignant cells from reactive, non-cancerous mesothelial cells that look similar under the microscope. Loss of MTAP on immunohistochemistry, like loss of BAP1, points strongly toward mesothelioma because reactive tissue keeps the protein. This makes MTAP a fast, inexpensive marker that supports a firm diagnosis, which matters both for treatment decisions and for a claim that depends on a confirmed diagnosis. When the stain is ambiguous, FISH testing for CDKN2A deletion can confirm the finding.

Example Sentence

The pathologist added an MTAP stain, and its loss in the tumor cells helped confirm mesothelioma rather than a benign reaction to the patient's prior pleurisy.

Related Terms

CDKN2A, BAP1, Immunohistochemistry, FISH, Mesothelioma, Diagnostic Biomarker

Notes

• Ask whether MTAP and BAP1 immunostains were performed; together they raise diagnostic confidence in difficult mesothelioma cases.
• Request that pathology reports and stained slides be preserved; they document the diagnosis your claim may rest on.
• If stains are equivocal, ask about FISH testing for CDKN2A (9p21) deletion as a confirmatory step.