Mesothelioma Misclassification

Mesothelioma misclassification is when a mesothelioma is wrongly identified as another cancer (or vice versa) on a pathology report. Because mesothelioma cells can look similar to lung adenocarcinoma, ovarian cancer, peritoneal carcinomatosis, or benign reactive mesothelial growths under the microscope, accurate diagnosis usually requires specialized immunohistochemical stains and review by a mesothelioma-experienced pathologist.

Origin

The recognition that mesothelioma is frequently misdiagnosed dates to the 1960s, when Wagner, Sleggs, and Marchand’s work in South Africa drew attention to a cancer that had often been recorded as lung cancer or carcinomatosis. The development of immunohistochemistry in the 1980s and consensus pathology guidelines from the International Mesothelioma Interest Group (IMIG) have since reduced, but not eliminated, the problem.

Significance in Asbestos Context

An accurate mesothelioma diagnosis is the foundation of both treatment decisions and any legal claim tied to asbestos exposure. If a tumor is misclassified as lung cancer, ovarian cancer, or simply "metastatic adenocarcinoma of unknown primary," patients may receive the wrong chemotherapy regimen, miss eligibility for mesothelioma-specific clinical trials, and lose access to asbestos trust funds and litigation claims that require a confirmed mesothelioma diagnosis. Conversely, a benign or reactive condition mistakenly read as mesothelioma can launch unnecessary treatment and litigation. Pathology review by a recognized mesothelioma center — using a standard panel of stains (e.g., calretinin, WT-1, D2-40, cytokeratin 5/6 versus claudin-4, MOC-31, BerEP4, TTF-1) and, increasingly, BAP1 and MTAP testing — is the accepted way to confirm or correct the diagnosis.

Example Sentence

After her oncologist noted that the original biopsy report was ambiguous, the family requested an expert pathology review at a mesothelioma program, which corrected an initial misclassification of "poorly differentiated adenocarcinoma" to epithelioid mesothelioma.

Related Terms

Immunohistochemistry, Epithelioid Mesothelioma, Sarcomatoid Mesothelioma, BAP1, Differential Diagnosis, Helsinki Criteria

Notes

• Ask whether your diagnosis was confirmed with a panel of immunohistochemical stains, and request the full pathology report (not just the summary) for your records.
• Consider obtaining a second opinion from a pathologist at a mesothelioma specialty center (such as an NCI-designated cancer center or a mesothelioma program) before starting treatment or filing a claim.
• Preserve the original tissue blocks and slides. These can be requested from the hospital pathology department and are essential for re-review, BAP1/MTAP testing, and any future legal proceedings.
• If an earlier cancer diagnosis (lung, ovarian, peritoneal) is in the family medical history and asbestos exposure is known, ask whether those slides should be re-examined for possible mesothelioma.