Breast Cancer Res Treat (2008) 109:567–572 Table 2 Deﬁnitions of outcome. Overall survival Disease speciﬁc survival Disease free interval Disease free survival Time from surgery until death from any cause Time from surgery until death related to breast cancer. Death not related to breast cancer is censored (Kaplan–Meier analysis) or treated as competing event (competing risk analysis). Time from surgery until recurrent disease.a Death not related to breast cancer is censored (Kaplan–Meier analysis) or treated as competing event (competing risk analysis). Time from surgery until recurrent diseasea or death from any cause. a In the deﬁnition of recurrent disease local recurrence, regional recurrence, and distant metastasis are considered events; contralateral breast cancer is ignored, treated as event or censored (Kaplan–Meier analysis) / treated as competing event (competing risk analysis) therapy or from subsequent recurrent disease. Breast cancer lesions at any other site, including the ipsilateral supra- clavicular lymph nodes, were classiﬁed as distant metas- tases. We classiﬁed death as disease related when death occurred in patients known with distant metastases. Otherwise we classiﬁed death as non-disease related. Survival probabilities were determined both by Kaplan– Meier method [7], and by competing risk analyses [8]. Competing risk analyses were calculated as described in ‘‘Tutorial in biostatistics: competing risks and multi-state models’’ by Putter et al. [8]. Results During median 10 years of follow-up 149 patients died. About 91 deaths were related to breast cancer, and another 58 patients died from causes unrelated to breast cancer. Local recurrences were diagnosed in 28 patients, regional recurrences in another 24. Distant metastases occurred in 111 patients, and in 30 patients breast cancer was diag- nosed in the contralateral breast. Estimated with the Kap- lan–Meier method, after 10 years of follow-up 68% of patients were still alive (overall survival). If no one had died from causes other than breast cancer, 79% of patients would have been alive (disease-speciﬁc survival) (Table 3). Disease free survival varied between 56% and 59%, depending on the deﬁnition of relapse. If no patients had died during follow-up, 65–69% of patients would have been free of recurrent disease (disease free interval) (Table 3). Compared with the competing risk approach, the Kaplan–Meier method slightly underestimated 10-year survival rates when one or more competing events were censored instead or ignored. The largest difference (2.0 percent-point) was found when both non-disease related death and contralateral breast cancer were censored (Table 3). Non-disease related death The difference in estimated survival probability between overall survival and disease speciﬁc survival and between disease free survival and disease free interval is by deﬁ- nition caused by the handling of non-disease related death. As older age is associated with a higher probability of non- disease related death, we evaluated the effect of patient’s Table 3 Estimated 10-year survival according to deﬁnition of survival determined both by Kaplan–Meier method and the competing risk analysis. 569 CR 73.7 51.6 64.9 65.4 63.4 123 Survival deﬁnition Overall survival Disease speciﬁc survival Disease free survival Contralateral BC ignored Contralateral BC censored Contralateral BC event Disease free interval Contralateral BC ignored Contralateral BC censored Contralateral BC event 10-year Survival (%) All patients KM 68.0 79.3 59.3 58.6 55.5 69.4 68.9 64.8 CR 80.6 59.4 70.9 70.9 66.5 KM 75.8 85.3 65.8 64.9 59.9 74.6 73.9 67.6 KM: Kaplan–Meier method; CR: competing risk analysis; BC: breast cancer No adjuvant systemic therapy Adjuvant systemic therapy CR 86.2 66.0 75.8 75.9 69.2 KM 58.6 71.9 51.2 51.1 50.2 63.0 63.2 61.3