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Here is an excerpt from an article on Measuring Proliferation in Breast Cancer:

The Ki67 labelling index is now widely used as the measure of proliferation. Ki67 is a protein expressed in the nucleus during the cell cycle [22]. Cells express the antigen during G1, S, G2 and M phases, but not during G0. The original antibodies raised against Ki67 required fresh or frozen tumour specimens. Cells that showed specific nuclear staining were scored as positive and the Ki67 labelling index was expressed as the percentage of the total number of tumour cells that stain positive; this equates to the growth fraction of the tumour. Higher grade cancers have higher Ki67 indices – one study found mean scores of 9% in grade I tumours, 14% in grade II and 26% in grade III [23]. The Ki67 index correlates significantly with estimates of the mitotic index [24] and SPF by flow cytometry [13,25,26], although some of the published correlation coefficients are modest (r = 0.42 [13], r = 0.22 [26]). Various studies have shown correlations between Ki67 and disease-free and overall survival, with an increased risk of recurrence in tumours with a high Ki67 [27-33]. Pierga and colleagues [34] performed a multivariate analysis and showed the Ki67-determined growth fraction to be an independent prognostic factor (p = 0.03) along with nodal status, age and adjuvant treatment received.

Hope this is useful.

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