Mitotic index and benefit of adjuvant anthracycline-based chemotherapy in patients with early breast cancer

Purpose We have evaluated whether the mitotic index could predict the benefit of adjuvant anthracycline-based chemotherapy in patients with early breast cancer who are eligible for adjuvant chemotherapy according to Saint Gallen guidelines. Patients and Methods A total of 937 patients from a single institution were included in two randomized trials that compared adjuvant anthracycline-based chemotherapy with no chemotherapy. These patients account for 83% of the overall population included in these trials. The first trial included premenopausal patients with node-negative disease, and the second one included postmenopausal patients, regardless of lymph node status. The treatment benefit was assessed according to the number of mitoses per field (X400). Results The mitotic index was assessable in 888 patients (94%). All the patients presented as either node-positive or an average-risk breast cancer according to 2003 Saint Gallen consensus conference guidelines. The 5-year overall survival rates were 91% and 87% for patients treated or not with adjuvant chemotherapy (P = .09). In patients with low/medium mitotic index (< three mitoses/field; n = 450), the 5-year overall survival rate was 95% for patients treated or not with adjuvant chemotherapy (P = .56). In patients with high mitotic index (>= three mitoses/field; n = 438), the 5-year overall survival rates were 86% and 79% for patients treated or not treated with,adjuvant chemotherapy, respectively (P = .02). Conclusion A high mitotic index is associated with the efficacy of adjuvant anthracycline-based chemotherapy in patients eligible for adjuvant chemotherapy in daily practice.