Standardized incidence ratios (SIR) comparing the incidence of CBC to the incidence of unilateral breast cancer, for CBC overall and for specific ER-status of first and second breast cancer, taking hormone therapy for the first cancer into account.

*ER-status of the second cancer was unknown for 29% of the CBC-patients.
The cohort is restricted to patients diagnosed after 1990, since hormone therapy is not recorded in the register before then. SIR calculations were stratified on hormone therapy treatment for first breast cancer and adjusted for age at first breast cancer in 5-year-categories and for period of first breast cancer in 10-year-categories.
SIR = Standardized incidence rate, CI = Confidence Interval, CBC = contralateral breast cancer, ER = Estrogen receptor.