Background: A randomised trial was conducted comparing wide lumpectomy and breast irradiation with modified radical mastectomy. As the follow-up was long (mean duration 22 years), we analysed the variation in the effect of treatment over time.
Patients and methods: The trial included 179 patients with a breast cancer measuring </=2 cm at macroscopic examination. Eighty-eight patients had breast-conserving surgery and radiotherapy, and 91 underwent mastectomy. All patients had axillary dissection. The analyses were based on Cox models with time-dependent treatment effects.
Results: The effect of treatment on death or metastasis did not vary with time. The risk of local recurrence was lower during the first 5 years for the breast-conserving surgery group as compared with the mastectomy group, but higher after 5 years (P = 10(-4) for a different treatment effect over time). Similar results were found in a database including 1847 patients with small breast tumours at diagnosis. In this analysis, late breast recurrences were also more frequent in the breast-conserving surgery group and this treatment effect was greater among younger patients (</=40 years at the time of diagnosis).
Conclusions: Late breast recurrences were more frequently observed in younger patients treated with breast-conserving treatment compared with those submitted to mastectomy. These results require confirmation in other randomised studies so that younger patients with early breast cancer can receive adequate counselling and so that a more stringent long-term follow-up policy can be adopted when breast-conserving treatment is planned.