Proliferation accurately identifies the high-risk patients among small, low-grade, lymph node-negative invasive breast cancers

Background: The proliferation factor mitotic activity index (MAI) is the strongest prognosticator in lymph nodenegative invasive breast cancer patients under age 71. The question remains, whether this also holds for ‘favourable prognosis’ subgroups. Patients and methods: The study was a multicentre prospective analysis of the MAI for recurrence-free survival and overall cancer-related survival of grade, MAI, and other prognosticators in 853 long-term follow-up, T1–3N0M0 breast cancer patients under 71 years. Results: In all tumours together (N = 853), in grade 3 (n = 269), in tumours <1 cm all grades (n = 84), 1–2 cm, grades 1 + 2( n = 300), and 2–3 cm, grades 1 + 2( n = 124), the MAI is prognostically superior. Other features [grade, estrogen receptor (ER), diameter, and age] did not enhance its prognostic value except in grades 1 + 2 tumours 2–3 cm diameter with MAI <10, where ER has an additional prognostic value. Conclusions: In women <71 years with T1–3N0M0 small or low-grade invasive breast cancer usually not receiving systemic treatment, MAI ‡10 accurately identifies those at high risk. These high-risk patients should be considered for adjuvant systemic therapy.