Mitotic index

Mitotic index is defined as the ratio between the number of a population's cells undergoing mitosis to its total number of cells.

Purpose

The mitotic index is a measure of cellular proliferation.[1]

It is defined as the percentage of cells undergoing mitosis in a given population of cells. Mitosis is the division of somatic cells into two daughter cells. Durations of the cell cycle and mitosis vary in different cell types. An elevated mitotic index indicates more cells are dividing. In cancer cells, the mitotic index may be elevated compared to normal growth of tissues or cellular repair of the site of an injury.[2] The mitotic index is therefore an important prognostic factor predicting both overall survival and response to chemotherapy in most types of cancer. It may lose much of its predictive value for elderly populations. For example, a low mitotic index loses any prognostic value for women over 70 years old with breast cancer.[3]

Calculation

The mitotic index is the number of cells undergoing mitosis divided by the total number of cells.[4]

A typical figure of mitotic index includes statements like "10 mitotic figures are noted per 10 high power fields" followed by "4 mitotic figures noted per 50 high power fields."

Formula



where (P+M+A+T) is the sum of all cells in phase as prophase, metaphase, anaphase and telophase, respectively and N is total number of cells.

References
  1. Rudolph; et al. (1998). "Correlation between mitotic and Ki-67 labeling indices in paraffin-embedded carcinoma specimens". Human Pathology. 29 (11): 1216–1222. doi:10.1016/s0046-8177(98)90248-9. PMID 9824098.
  2. Urry; et al. (2014). Campbell Biology in Focus. Pearson.
  3. Baak, J. P. A.; Gudlaugsson, E.; Skaland, I.; Guo, L. H. R.; Klos, J.; Lende, T. H.; Søiland, H. V.; Janssen, E. A. M.; Zur Hausen, A. (2008). "Proliferation is the strongest prognosticator in node-negative breast cancer: Significance, error sources, alternatives and comparison with molecular prognostic markers". Breast Cancer Research and Treatment. 115 (2): 241–254. doi:10.1007/s10549-008-0126-y. hdl:1956/5701. PMID 18665447.
  4. Edexcel practical materials created by Salters-Nuffield Advanced Biology, copyright University of York Science Education Group


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