BACKGROUND AND PURPOSE:Early-stage breast cancer is increasing and consequently the use of breast-conserving surgery (BCS). We examined the effect of mastectomy and BCS on overall and breast cancer survival in routine health care in Geneva, Switzerland.PATIENTS AND METHODS:We included all stage I breast cancers treated by surgery (n=1046) recorded at the Geneva Cancer Registry between 1988 and 1999. The effect of treatment type was evaluated by Cox models, which accounted for confounders.RESULTS:Overall, 780 (75%) women had BCS with radiotherapy, 57 (5%) BCS alone and 209 (20%) mastectomy. The overall 10-year survival was 86, 56, and 72%, respectively. The effect of BCS with radiotherapy was similar to that of mastectomy for both breast cancer mortality (adjusted hazard ratio (HR), 0.67; 95%CI, 0.31-1.38) and other causes of mortality (HR, 0.79; 95%CI, 0.49-1.28). Women with BCS alone had higher mortality from breast cancer (HR, 3.95; 95%CI, 1.59-9.84).CONCLUSIONS:This retrospective study shows that BCS plus radiotherapy is the predominant treatment in routine practice for stage I breast cancer in Geneva, with the same effect on survival as mastectomy. In this data set the addition of radiotherapy to BCS substantially reduces mortality from breast cancer without increasing other causes of mortality after 10 years of follow-up.