The prognostic value of the mitotic activity index in patients with primary breast cancer who were not treated with adjuvant systemic therapy

Background. At the St Gallen meeting of 2001 it was agreed to select high-risk patients for adjuvant systemic therapy by lymph node status, tumor size, age, hormone receptor status, and histological grade. In The Netherlands it was chosen to use either the histological grade or the mitotic activity index (MAI). The aim of this study was to retrospectively evaluate the independent prognostic value of the MAI in primary breast cancer patients, who were not treated with adjuvant systemic therapy, on relapse-free survival (RFS) and overall survival (OS). Patients and methods. The data of 137 systemically untreated patients with primary breast cancer diagnosed between 1992 and 1996, of whom MAI was assessed, were retrospectively collected. The MAI was correlated to classical prognostic factors and we determined the prognostic value of the MAI, the histological grade and other prognostic factors. Results. The median observation time was 4.2 years. The MAI showed a positive correlation to lymph node status (P < 0.001) and a negative correlation to age (P = 0.005), menopausal status (P < 0.001) and the ER and PgR status (r(s) = 0.390 [ER], r(s) = 0.440 [PgR], both P < 0.001). A high MAI (>= 15) predicted a reduced RFS and OS in the Kaplan-Meier analysis (P = 0.0070 and P = 0.0017, respectively). Also in the multivariate analysis, the MAI showed to be an independent predictor of poor RFS (P = 0.035), in addition to lymph node status. However, the MAI did not predict for OS, in contrast to tumor size and lymph node status. Conclusion. The present study confirms that the MAI is an independent prognostic factor for RFS, but not for OS and may be useful for daily clinical practice.