Breast conserving treatment in Denmark, 1989-1998. A nationwide population-based study of the Danish Breast Cancer Co-operative Group

Background. Randomised studies have shown that breast conserving surgery followed by radiotherapy is associated with a prognosis similar to mastectomy alone. This formed the basis for recommending breast conserving surgery combined with radiotherapy as a standard treatment for suited breast cancer patients in Denmark. Patients and methods. To evaluate the results of this treatment, we performed a nationwide population-based follow-up study of patients aged less than 75 years treated in Denmark from 1989 to 1998 based on the database of Danish Breast Cancer Cooperative Group. Results. At 15 years of follow-up, the Kaplan-Meier estimate of overall survival was 69% among 3758 patients who received the recommended treatment. Within the first 10 years of follow-up, the cumulative incidences of loco-regional recurrences, distant metastases or other malignant disease, or death as a first event were 9.0, 19.9, and 6.0% respectively, when analysed in a competing risk setting. The risk of loco-regional recurrences was significantly decreased in patients aged 50 years or more and increased with increasing tumour size. There was a pronounced beneficial effect of adjuvant radiotherapy with those not receiving radiotherapy having a hazard ratio of 3.52 (95% CI 2.21-5.61). The effect of resection margins was significant for loco-regional recurrences only in node negative patients. Conclusion. In conclusion, the present study shows that results similar to those from randomised clinical trials can be obtained when breast conserving treatment is applied as a standard treatment in an entire population.