Breast surgery in the ‘Arimidex, Tamoxifen Alone or in Combination’ (ATAC) trial

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Abstract
BACKGROUND: Various factors affect patients' decisions regarding whether to undergo surgery for the treatment of early‐stage breast carcinoma. The ‘Arimidex, Tamoxifen Alone or in Combination’ (ATAC) trial, the largest multinational randomized trial of adjuvant therapy for patients with operable breast carcinoma to date, offers the opportunity to investigate whether nationality is one such factor.METHODS: After receiving primary therapy for early‐stage breast carcinoma, 9366 women (from a total of 21 countries) were randomized to receive anastrozole, tamoxifen, or anastrozole plus tamoxifen for 5 years. In the current study, mastectomy and breast conservation rates were compared among participating countries. The possibility that variations from country to country could be explained by inequalities in terms of pathologic, clinical, and hospital‐related correlates of surgical choice was explored first on univariate analysis and then on multivariate logistic analysis.RESULTS: National mastectomy rates ranged from 20% to 97%; 51% of the 2222 enrollees from the United States had undergone mastectomy, compared with 42% of the 3228 enrollees from the United Kingdom (odds ratio [OR], 1.43; 95% confidence interval [CI], 1.28–1.60;P< 0.001). On univariate analysis, larger tumor size, positive lymph node status, higher tumor grade, older age, and adjuvant chemotherapy use were found to be correlated with mastectomy use. In contrast, positive hormone receptor status, increased body weight, and enrollment at a center that had more than 40 enrollees were found to be associated with breast conservation. The same correlates were identified on multivariate logistic analysis (P< 0.05), except that the number of enrollees at a patient's treatment center no longer possessed predictive value. After correction for these correlated factors, residence in the United States (compared with residence in the United Kingdom) remained an independent predictor of mastectomy use (OR, 1.44; 95% CI, 1.26–1.64;P< 0.001).CONCLUSIONS: American women enrolled in the ATAC trial were more likely to undergo aggressive surgery compared with their counterparts from the United Kingdom. More generally, nationality was found to be an independent determinant of surgical choice in the current study. Cancer 2004. © 2004 American Cancer Society.