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 3 758 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.