Trends in breast cancer treatment in Korea and impact of compliance with consensus recommendations on survival

Although some studies suggest that conformity with consensus recommendations for breast cancer therapy is associated with increased survival, the data are not clear. We identified patients in four hospital-based breast cancer registries in Korea who had undergone primary curative surgery (stage 0-III) from 1993 through 2002 (n = 8,407). We collected demographic and clinical characteristics such as age, stage, treatment, and hormone receptor status. We gathered 1993-2004 mortality data by linkage to the National Statistical Office. During the follow-up period of 43,145 person-years (mean, 5.13 years), we identified 899 deceased cases. We used the standard Poisson regression model to estimate the hazard ratio (HR) for survival in relation to conformity with guidelines for chemo-, hormone, and locoregional therapy. Guideline compliance for systemic therapy increased from 24.0% in 1993 to 83.8% in 2002. Among mastectomy patients with <4 positive lymph nodes and tumors <5 cm, post-mastectomy radiotherapy was associated with poor survival (HR 2.07; 95% CI: 1.53-2.81). Tamoxifen use was associated with better survival among patients with hormone receptor-positive tumors (HR 0.57; 95% CI: 0.45-0.73) and with poorer survival among hormone receptor-negative patients who had affected nodes (HR 1.58; 95% CI: 1.01-2.44). Relative to conformity, non-conformity with both chemo- and hormone therapy guidelines was associated with a 76% higher risk of death. Compliance with consensus recommendations for chemo- and hormone therapy is significantly associated with better survival. Overuse of post-mastectomy radiotherapy and tamoxifen beyond the consensus recommendations may be harmful.