Mitotic Count

Mitotic count is the number of cells actively dividing (in mitosis) that a pathologist sees when examining a tumor sample under the microscope, usually reported per 10 high-power fields or per square millimeter. A higher mitotic count generally means the tumor is growing more aggressively. It is one of several features pathologists use to grade mesothelioma and other cancers.

Origin

The term comes from "mitosis," coined in 1882 by German anatomist Walther Flemming from the Greek mitos (thread), describing the thread-like chromosomes visible during cell division. Counting mitotic figures has been a core part of tumor grading since the early 20th century and was formally incorporated into mesothelioma grading systems beginning in the 2010s.

Significance in Asbestos Context

For patients with epithelioid mesothelioma, the mitotic count is part of a two-tier nuclear grading system (combined with nuclear atypia) that helps predict how the cancer is likely to behave. A low mitotic count combined with mild nuclear features generally suggests a slower-growing tumor and longer survival, while a high count signals more aggressive disease that may warrant more intensive treatment. This number often appears in the surgical pathology report and can influence decisions about surgery, chemotherapy, immunotherapy, and clinical trial eligibility, and it may also be referenced by medical experts when discussing prognosis in a legal claim.

Example Sentence

The pathology report listed a mitotic count of 2 per 2 mm², which placed her epithelioid mesothelioma in the low-grade category and supported her oncologist's recommendation for aggressive multimodal treatment.

Related Terms

Nuclear Atypia, Nuclear Grade, Epithelioid Mesothelioma, Ki-67, Histologic Grade, Pathology Report

Notes

• Ask your oncologist or pathologist to explain where your mitotic count falls and how it factors into your nuclear grade (low vs. high) for epithelioid mesothelioma.
• Request a full copy of your surgical pathology report and any addenda; the mitotic count and grade are often buried in the microscopic description or comment section.
• If your case is being reviewed for a clinical trial or second opinion, send the original slides, not just the report, because mitotic count can vary between pathologists and may be re-scored at a specialty center such as a mesothelioma program at an NCI-designated cancer center.
• Preserve all pathology reports, slides, and tissue blocks; these materials are important both for ongoing treatment decisions and for documenting disease severity in a legal claim.