Reactive Mesothelial Cells

Reactive mesothelial cells are normal cells lining the pleura, peritoneum, and pericardium that have become enlarged and multiplied in response to irritation, inflammation, or injury. Under the microscope they can look atypical and sometimes resemble cancer cells, even though they are benign. They are commonly seen in fluid samples from patients with a wide range of conditions, including asbestos-related pleural disease.

Origin

The term comes from "mesothelium," the thin membrane lining body cavities (from Greek mesos, middle, and epithelium), combined with "reactive," meaning responding to a stimulus. Pathologists began distinguishing reactive from malignant mesothelial proliferations in the early 20th century, and the distinction became critically important with the rise of mesothelioma diagnoses linked to asbestos exposure.

Significance in Asbestos Context

For patients with asbestos exposure, the appearance of reactive mesothelial cells in pleural fluid or a biopsy is a common but ambiguous finding. Because asbestos fibers irritate the pleura for decades, the lining cells can become atypical-looking, and telling reactive change from early epithelioid mesothelioma is one of the hardest problems in pathology. This is why a single cytology report saying "reactive mesothelial cells" should never be assumed to rule out mesothelioma. Additional tissue biopsy, immunohistochemical stains (such as BAP1, MTAP, and desmin), and sometimes FISH testing are often needed to make a definitive call. In medical records, repeated findings of reactive mesothelial cells over months or years in someone with an asbestos history may be an early warning that warrants closer follow-up.

Example Sentence

The patient's first thoracentesis showed only reactive mesothelial cells, but because of his shipyard exposure history, his pulmonologist ordered a thoracoscopic biopsy that ultimately confirmed epithelioid mesothelioma.

Related Terms

Mesothelioma, Pleural Effusion, Cytology, Immunohistochemistry, BAP1, Thoracentesis

Notes

• If a cytology report mentions "reactive mesothelial cells" and you have a known asbestos exposure history, ask your doctor whether a tissue biopsy and immunohistochemistry (especially BAP1 and MTAP stains) should be performed to rule out mesothelioma.
• Request that any pleural fluid or biopsy slides be preserved. These materials may need to be re-reviewed by a mesothelioma-specialist pathologist, and they can also become important evidence in a legal claim.
• Keep copies of every pathology and cytology report; a pattern of repeated "reactive" findings before a cancer diagnosis can be relevant to documenting when disease actually began.
• Consider a second pathology opinion at a center experienced in mesothelioma (such as an NCI-designated cancer center) before accepting either a benign or malignant diagnosis based on cytology alone.