Reactive Cells

Reactive cells are normal body cells (usually mesothelial cells lining the pleura or peritoneum, or immune cells) that have changed in appearance because of inflammation, fluid buildup, or injury. Under the microscope they can look enlarged or irregular, which sometimes makes them difficult to distinguish from cancer cells. In the asbestos context, the most important challenge is telling reactive mesothelial cells apart from mesothelioma cells.

Origin

The term comes from pathology, where "reactive" has long been used to describe cells responding to a stimulus such as inflammation or irritation, in contrast to "neoplastic" cells that are growing abnormally on their own. The distinction became clinically critical in the 20th century as pleural effusions and biopsies were increasingly examined for mesothelioma.

Significance in Asbestos Context

For patients being evaluated for mesothelioma, the question of "reactive versus malignant" is one of the hardest calls in pathology. Asbestos exposure, pleural effusions, and chronic inflammation can all cause mesothelial cells to look atypical, and an initial cytology report may describe "atypical mesothelial cells, cannot exclude malignancy" or "reactive mesothelial proliferation." This kind of inconclusive reading often delays diagnosis and may require additional testing (immunohistochemistry (such as BAP1 and MTAP staining), FISH testing, or a surgical biopsy) before a definitive answer is reached. In legal proceedings, defense experts sometimes argue that findings in a patient's records reflect reactive changes rather than cancer or rather than asbestos-related disease, so the wording in pathology reports matters.

Example Sentence

The first pleural fluid sample showed only reactive cells, so her pulmonologist ordered a thoracoscopic biopsy to get a definitive diagnosis.

Related Terms

Mesothelial Cells, Atypical Mesothelial Hyperplasia, Cytology, Immunohistochemistry, BAP1, Pleural Effusion

Notes

• If a pathology or cytology report describes "reactive" or "atypical" cells without a clear diagnosis, ask whether additional testing (BAP1 immunostain, MTAP immunostain, CDKN2A FISH) or a tissue biopsy is warranted.
• Request that all slides and blocks be preserved and, when diagnosis is uncertain, sent for expert mesothelioma pathology review at a specialty center (e.g., a National Cancer Institute–designated center).
• Keep copies of every pathology report, including the early "reactive" or "indeterminate" ones, because the diagnostic timeline can become important in both treatment planning and any later legal claim.
• Ask your doctor specifically whether the findings are being called reactive, atypical, in situ mesothelioma, or invasive mesothelioma, since these have very different implications for treatment and prognosis.