The system recognizes that mitotic rate per area is a strong predictor and essentially standardizes the cut-points (3 and 8 mitoses/mm 2) to two separate mitotic rates (mitoses/area), creating a three tier system. The procedure for counting mitoses was laid-out in the original paper that described the scoring system, and has subsequently been clarified in the CAP protocol, where it states it should be done on the “most mitotically active area”. In breast pathology, mitotic counts are a part of the Nottingham score and have been demonstrated to be a histomorphologic predictor of outcome. The later factor is not a significant factor if one frames the problem as an assessment of the poorly differentiated region of the tumour (as opposed to the tumour as a whole). The former introduces a systematic bias that consistently skews the results in the direction towards a higher mitotic score. As cellularity is time consuming to quantify, mitoses/area is often used instead of mitoses/cell.Ĭonsidered as a sampling problem, mitotic counting is, typically biased in a number of ways: (1) many pathologists do not start the count until they have found one mitosis, (2) pathologists count mitoses in the area of the tumour they consider to be the most mitotically active (usually the most poorly differentiated portion). As mitotic figures are rare in relation to the number of cells, 10 high power fields (HPF) of view are typically examined.
Mitotic counts are performed by a pathologist, counting mitotic figures at a high magnification. Thus, mitotic counts are used in a wide number of neoplasms to predict prognosis, and highly proliferative neoplasms (with many mitoses) usually have a worse prognosis. Tumour growth rate is a prognostic marker and can be evaluated by its correlate at the cellular level: mitoses.