Original Article
The utility of mitotic index, oestrogen receptor and Ki-67 measurements in the creation of novel prognostic indices fornode-negative breast cancer

https://doi.org/10.1053/ejso.1999.0657Get rights and content

Abstract

Introduction:Prognostic factors can be useful to identify node-negative patients at increased risk of relapse who should receive adjuvant treatment. In the past, oestrogen receptor status and mitotic index have been shown to be significant predictors of prognosis. Different techniques for the measurement of these prognostic factors are available.Methods:Paraffin-embedded tumour specimens from 441 pre-menopausal patients with node-negative breast cancer who were previously randomized onto a trial comparing peri-operative chemotherapy with no further therapy were studied. Oestrogen receptor status was determined by the classical biochemical assay and by immunohistochemistry (ER-IA). Mitotic index was assessed by counting the number of mitoses and by calculating the percentage of tumour cells positively staining for the antibody Ki-67.Results:There was a good correlation between ER-IA and the biochemical ER-assay (P<0.01), and the percentage of Ki-67 positive tumour cells and mitotic counts (P<0.01) respectively. However, ER-IA significantly predicted disease-free survival (RR=2.67, 95% CI: 1.60–4.44,P<0.01) whereas the biochemical assay was only borderline significant (RR=1.54, 95% CI: 1.00–2.36,P=0.05). Similarly, Ki-67 was a stronger indicator of prognosis (RR=2.84, 95% CI: 1.80–4.48,P<0.01) than mitotic counts (RR=1.56, 95% CI: 1.22–2.00,P<0.01).Conclusions:We conclude that ER-IA performs better in predicting prognosis than the classical biochemical oestrogen receptor assay. Ki-67 is a more accurate marker for tumour cell proliferation and predicts prognosis of patients with breast cancer better than do mitotic counts.

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The authors are from the European Organization for Research and Treatment of Cancer, EORTC Breast Cancer Co-operative Group.

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Correspondence to: Marc J. van de Vijver, MD, PhD, Netherlands Cancer Institute, Department of Pathology, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands. Fax: +31-20-512 27 59, E-mail: [email protected]

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