568 and B20 trials both non-disease related death, contralat- eral breast cancer, and second primary cancer were in- cluded as events in the deﬁnition of disease free survival [3, 4]. In a recent report with long-term ﬁndings the deﬁnition of recurrence free survival was restricted to local or regional recurrence, or distant metastasis only [5]. Despite these different deﬁnitions, many papers on breast cancer survival do not provide an explicit deﬁni- tion of recurrent disease. A review on prognostic factors in node-negative breast cancer was published in 2002 by Mirza et al. [6]. In the methods section of their report, they stated that only papers in which overall or disease free survival were speciﬁed were included in their re- view. Sixty-three papers from their reference list dealt with survival analysis in primary breast cancer. We re- viewed the deﬁnitions of recurrent disease used in these 63 papers. In only 21 out of 47 papers that studied time to recurrent disease the deﬁnition of recurrent disease explicitly described the handling of non-cancer related mortality. Intercurrent deaths were censored in 14 papers and counted as events in 7 papers. Eight papers explicitly described the handling of contralateral breast cancer. Contralateral breast cancer was censored in 1 and con- sidered as event in 7 papers. The handling of second primary cancer was described in 7 papers. Second pri- mary cancer was censored in 2 and counted as event in 5 papers. In most papers the survival probability is estimated with the Kaplan–Meier method from observed survival times, censored or uncensored [7]. Censoring may arise due to end of follow-up, loss to follow-up, but also due to a competing event. The Kaplan–Meier method requires non- informative censoring, which means that those individuals who are censored should be as likely to have the sub- sequent event of interest as those who remain in the study. In particular competing events, such as: contralateral breast cancer or non-disease related death, might cause informa- tive censoring. For this reason others have propagated an approach that accounts for informative censoring in sur- vival analyses in the presence of competing events, a competing risk analysis [8–11]. The main objective of this study is to analyse the effect of various deﬁnitions of survival and relapse on prediction of outcome in patients with early breast cancer. Thereby, we focus on the inﬂuences of non-disease related death and contralateral breast cancer. Data from a (prospec- tively determined) cohort of 463 patients with primary breast cancer were used to evaluate the effects of various deﬁnitions of survival and relapse. A second objective was to compare the value of competing risk analysis with that to that of the Kaplan–Meier method for survival analysis. 123 Breast Cancer Res Treat (2008) 109:567–572 Material and methods Between October 1989 and March 1993 463 patients diagnosed with operable, stage I to III breast cancer agreed to participate in a prospective registration study on prog- nostic factors. We obtained written informed consent from all patients. Surgery, radiotherapy and adjuvant systemic treatment were given according to the guidelines of the Comprehensive Cancer Centre Middle Netherlands. Pa- tient-, tumour- and treatment characteristics are shown in Table 1. We assessed follow-up data until December 2002. The events that were used to determine the different deﬁnitions of outcome were local- and regional recurrent disease, contralateral breast cancer, distant metastasis, disease related death and non-disease related death. In the various analyses these events were either ignored, consid- ered as event of interest or as competing event (censored), depending on the various deﬁnitions of outcome. Deﬁni- tions of overall survival, diseases speciﬁc survival, disease free interval, and disease free survival are given in Table 2. We deﬁned local recurrent disease as either recurrence in the skin or soft tissue of the (ipsilateral) chest wall or in the ipsilateral breast. Regional recurrent disease conﬁned recurrence in the lymph nodes in the ipsilateral axilla, in- fraclavicular fossa or internal mammary chain. Contralat- eral breast cancer included invasive breast cancer lesions in the contralateral breast regardless of histological type, lymph node involvement, and time interval from initial Table 1 Patient-, tumour-, and treatment characteristics Number of patients (%) Age £50 year 51–70 year >70 year Primary surgical therapy Breast conserving therapy Modiﬁed radical mastectomy Other Adjuvant systemic therapy Hormonal therapy Chemotherapy Histology Ductal Other Tumour size £ 20 mm > 20 mm Axillary lymph nodes Negative Positive 142 (31) 213 (46) 108 (23) 266 (57) 190 (41) 7 (2) 142 (31) 72 (16) 290 (63) 173 (37) 272 (59) 191 (41) 278 (60) 185 (40)