Aims: The Mitotic Activity Index (MAI) is a strong prognostic factor for disease free survival in breast cancer. The MAI is lower in screen detected tumours, correlating with less aggressive biological behaviour in this group. In this study the MAI is compared between screen detected, interval and symptomatic breast cancers.
Methods: Between 1991 and 1999, the MAI was determined in 581 breast cancers, 160 were detected by screening, 66 were interval carcinomas, and 355 were symptomatic breast cancers. Other prognostic factors were also registered.
Results: The interval group had a significantly higher median MAI (17-18, range 1-134) than the screen detected group (7-8, range 0-94,P <0.0001). There was no difference with the symptomatic group (MAI 15, range 0-149,P =0.92).
Conclusions: Interval cancers had an intermediate outcome when correlated with other prognostic factors, compared to screen detected and symptomatic cancers.