Hazard rates of recurrence following diagnosis of primary breast cancer

We calculated hazard rates for recurrence in patients with primary breast cancer (stage I, II; no adjuvant therapy). Previous publications have indicated a peak in hazard rates for recurrence (or death) at approximately 2-3 years after diagnosis of primary breast cancer. However, there have been conflicting reports concerning the presence of a second peak at 5-7 years after diagnosis. In this study, we estimated hazard functions by the Nelson-Aalen method and fit by cubic-linear and cubic-cubic-linear models to test for the presence of one or two peaks, respectively. We identified two peaks in hazard of recurrence, one at 2 years and another at 5 years. The 5-year peak, though statistically significant, represents very small differences in patient outcome. This additional peak may be an artifact of interval censoring due to a tendency to follow-up patients at specific bench-mark time points.