The prognostic relevance of estimates of proliferative activity in early breast cancer

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Abstract
Aims: Immunohistochemical estimates of cell proliferation evaluated with MIB‐1 antibody have been suggested as prognostic indicators in different types of carcinoma. This study investigates whether MIB‐1 scores add additional prognostic impact when evaluated together with classical clinicopathological parameters at diagnosis in early breast cancer patients. Materials and methods: Tumour specimens from 365 consecutively treated breast cancer patients were immunostained for MIB‐1 and evaluated under the microscope using systematic random sampling accomplished by the CAST‐grid system. Results: The systematic random sampling technique resulted in MIB‐1 estimates with very high interobserver and intraobserver reproducibilities (P < 0.0001). Median MIB‐1 was 16% (range 0–83%). Patients were stratified by MIB‐1 in tertiles, and increasing MIB‐1 was significantly associated with poor overall and disease‐specific survival in node‐positive patients, but not in node‐negative patients. High MIB‐1 was significantly related to large tumour size, and strongly associated with high grade, high mitotic score, negative oestrogen receptor status and young age. In multivariate analysis, both with and without malignancy grade and number of mitoses included in the analysis, MIB‐1 estimates showed no independent prognostic impact. Conclusions: High MIB‐1 estimates did not add independent prognostic information at diagnosis when evaluated together with classical prognostic markers of early breast cancer.