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.
For example, a low mitotic index loses any prognostic value for women over 70 years old with breast cancer.
In a clinical setting, and where the intention is only to compare observations rather than to state an index, informal alternatives may be used: for example "12 mitotic figures are noted per 10 high power [microscopic] fields" in contrast with "4 mitotic figures noted per 50 high power fields."
Mitosis is also required at a higher rate to grow and repair tissue.
Plants have higher rates of mitosis at the cells of the shoot and root tips.