Counting mitoses: SI(ze) matters!

Ian A. Cree*, Puay Hoon Tan, William D. Travis, Pieter Wesseling, Yukako Yagi, Valerie A. White, Dilani Lokuhetty, Richard A. Scolyer

*Corresponding author for this work

Research output: Contribution to journalReview articleAcademicpeer-review


Mitoses are often assessed by pathologists to assist the diagnosis of cancer, and to grade malignancy, informing prognosis. Historically, this has been done by expressing the number of mitoses per n high power fields (HPFs), ignoring the fact that microscope fields may differ substantially, even at the same high power (×400) magnification. Despite a requirement to define HPF size in scientific papers, many authors fail to address this issue adequately. The problem is compounded by the switch to digital pathology systems, where ×400 equivalent fields are rectangular and also vary in the area displayed. The potential for error is considerable, and at times this may affect patient care. This is easily solved by the use of standardized international (SI) units. We, therefore, recommend that features such as mitoses are always counted per mm2, with an indication of the area to be counted and the method used (usually “hotspot” or “average”) to obtain the results.
Original languageEnglish
Pages (from-to)1651-1657
Number of pages7
JournalModern Pathology
Issue number9
Early online date2021
Publication statusPublished - Sep 2021

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