Multivariate prognostic evaluation of the mitotic activity index and fibrotic focus in node-negative invasive breast cancers

We validated with univariate and multivariate (Cox) analysis, the prognostic value of the mitotic activity index (MAI), the fibrotic focus (FF) and other prognosticators in 448 patients with lymph node-negative (LN−) invasive breast cancer <55 years without adjuvant systemic treatment (72.5 months median follow-up, range 4-119). Of these patients, 24.8% developed distant and 1.6% loco-regional recurrence. FF showed excellent inter-observer reproducibility (κ = 0.93). Strong prognosticators were MAI, grade, nuclear atypia, FF and the St. Gallen criterion (SG). The subgroup with excellent survival selected by SG was only 16% of all patients, implying over-treatment of more than 70% of all LN− patients when using SG as adjuvant therapy selection criterion. If MAI <10, 13% showed distant metastases, contrasting with 41% if MAI ⩾10. FF was prognostic in the ductal and mixed ductal cancers, but not in the lobular and other subtype cancers. Patients with invasive (mixed) ductal cancers with FF absent, FF < 1/3 or FF > 1/3 of the tumour area, had distant metastasis rates of 17%, 35% and 48%; in MAI < 10 and FF absent, FF < 1/3 or FF > 1/3, metastasis rates were 11%, 13% and 42% and if MAI ⩾ 10, metastasis rates were 31%, 48% and 50%, respectively. In the 12 patients with MAI < 10 and a large FF > 1/3, event-free survival was similar to patients with MAI ⩾ 10. With multiple regression MAI < 10 versus ⩾10 is the strongest prognosticator (also stronger than the SG). The FF may be important as it has additional prognostic value to the MAI in the small subgroup of invasive ductal or mixed-ductal breast cancer patients with combined MAI < 10 and an FF > 1/3 of the tumour area.