The Mitotic Activity Index in combination with Her2neu: a strong prognosticator in breast cancer

The aim of this study is to evaluate the prognostic value of the Mitotic Activity Index (MAI) in combination with the human epidermal growth factor receptor (Her2) for distant metastases-free survival (DMFS) and disease-specific survival (DSS) in breast cancer and compare it with the immunohistochemically (IHC) profile types.

Analyses were based on 2.923 breast-conserving breast cancer specimens with known MAI, Her2 status, and hormone receptor status, resulting in 2.678 Her2MAI combinations, MAI ≤ 12/Her2negative, MAI > 12/Her2negative, MAI > 12/Her2positive, and MAI ≤ 12/Her2positive, and 2.560 IHC profile types, luminal A, luminal B, triple negative, and non-luminal Her2positive.

For DMFS, the MAI > 12/Her2negative combination showed a significantly worse outcome in multivariate analyses compared to the MAI ≤ 12/Her2negative combination. None of the IHC profile types showed significantly different outcomes for DMFS and DSS as compared to luminal A. We performed a separate analysis on age and lymph node status. The significance of MAI > 12/Her2negative seems to be limited to women ≤ 55 years for both DMFS and DSS. However, with respect to DSS, this seems to be limited to node negative cases. The IHC profile types for DSS, luminal B showed a significantly worse outcome for women > 55 years compared to that for luminal A, although it showed rather wide confidence interval.

The MAI > 12/Her2negative combination seems to be a strong prognosticator for DMFS and DSS, particularly for women ≤ 55 years. However, none of the IHC profile types seems to be a prognosticator in breast cancer.