Purpose: To determine whether estrogen replacement therapy (ERT) alters the development of new or recurrent breast cancer in women previously treated for localized breast cancer.
Patients and methods: Potential participants (n = 319) in a trial of ERT after breast cancer were observed prospectively for at least 2 years whether they enrolled onto the randomized trial or not. Of 319 women, 39 were given estrogen and 280 were not given hormones. Tumor size, number of lymph nodes, estrogen receptors, menopausal status at diagnosis, and disease-free interval at the initiation of the observation period were comparable for the trial participants (n = 62) versus nonparticipants (n = 257) and for women on ERT (n = 39) versus controls (n = 280). Cancer events were ascertained for both groups.
Results: Patient and disease characteristics were comparable for the trial participants versus nonparticipants, as well as for the women on ERT versus the controls. One patient in the ERT group developed a new lobular estrogen receptor-positive breast cancer 72 months after the diagnosis of a ductal estrogen receptor-negative breast cancer and 27 months after initiation of ERT. In the control group, there were 20 cancer events: 14 patients developed new or recurrent breast cancer at a median time of 139.5 months after diagnosis and six patients developed other cancers at a median time of 122 months.
Conclusion: ERT does not seem to increase breast cancer events in this subset of patients previously treated for localized breast cancer. Results of randomized trials are needed before any changes in current standards of care can be proposed.