Abstract P6-13-03: Local Treatment Strategies in Young and Elderly Stage IV Breast Cancer Patients in the USA and The Netherlands

Abstract

Abstract Introduction Approximately 5-10% of breast cancer patients present with stage IV at diagnosis. The appropriate treatment is still under debate. This study focused on differences in treatment regimens between the United States (USA) and the Netherlands (NL) within age groups. Methods As we included data from NL and the USA, we were able to construct an instrumental variable as a substitute for randomization and get around selection bias. We compared Dutch and USA treatment strategies; restrictive versus more often extensive local therapy. Data from the NL Cancer Registry and the US Survaillance, Epidemiology and End Results Program were used to construct a database for analyses. All primary stage IV breast cancer patients diagnosed in 1995-2003 were included. Follow up cutoff date was 12- 31-2005 (USA) and 12-31-2008 (NL). Analyses were stratified by age (<65, 65-75 and ≥75 years). Chi Square Tests were performed for therapy rates, overall survival was calculated by Cox Proportional Hazard Analyses. Results A total number of 11030 patients were included (5354 NL, 5676 USA). Within each age category, surgery was applied more often in the USA (<65: NL37%-USA52%, P<0.001. 65-75: NL28%-USA42%, P<0.001. ≥75: NL21%-USA39%, P<0.001). Similar results were observed for use of radiotherapy after surgery (<65: NL30%-USA47%, P<0.001. 65-75: NL26%-USA44%, P<0.001. ≥75: NL 17%-USA36%, P<0.001). Rate of radiotherapy without surgery did not differ between the two countries. With increasing age, use of surgery and use of radiotherapy after surgical treatment decreased (NL, USA each P<0.001). Use of radiotherapy without surgical intervention however increased with age in both countries (NL p=0.002, USA p=0.001). Although unadjusted analysis showed enhanced overall survival for patients <65 years of age in the USA compared to NL (HR 0.92 (0.86-0.98), p=0.006), these results were not confirmed in multivariable analyses. Patients ≥75 years of age in the USA compared to NL, however, had worse overall survival, confirmed in multivariable analyses (HR 1.17 (1.08-1.27), P<0.001). Conclusion Surgery and radiotherapy after surgical treatment for stage IV breast cancer patients was applied more often in the USA compared to NL in all age categories. Use of local therapy decreased with increasing age. In multivariable analyses, patients ≥75 years of age had a worse overall survival in the USA. This finding suggests that a more extensive local treatment strategy does not improve overall survival in this group of elderly patients. The opposite was true for young patients, although these results were not confirmed in multivariable analyses. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P6-13-03.