The use of adjuvant chemotherapy in the ATAC trial: Nationality correlates with the use of chemotherapy

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597 Background: The ATAC trial in 1996–2000, randomized 9366 postmenopausal women, from 21 countries, with early stage breast cancer, to adjuvant therapy with anastrozole, tamoxifen or the combination after primary surgery +/- radiotherapy +/- chemotherapy. Although there was an equal distribution of prognostic and therapeutic factors across treatment arms, there were marked differences in the use of adjuvant chemotherapy between participating countries (2–65%). Methods: A retrospective analysis was done looking for features which predicted for receiving chemotherapy in addition to the protocol-determined hormonal therapy to see if national differences could be explained. Results: In a univariate analysis (p<.05) node positivity (particularly>4), tumor size>2 cm, poorly differentiated tumors, ER negative receptor status, and use of mastectomy predicted for receiving chemotherapy. Older age predicted for not receiving chemo. Using the United States (n=2222, 33% chemotherapy rate) as a standard, in a multivariate analysis including all potential predictive factors, nationality remained predictive for the use of chemotherapy. All countries except three had a significantly (p<.05) lower usage of chemotherapy than the US. Three groups were identified: those with a with an odds ratio of less than 0.1 versus the US (8 of 21 nations including the United Kingdom & Germany, adjusted chemo usage rate <5%) those with an odds ratio of 0.1- 0.5 (n=9 including France, Canada, Sweden, adjusted chemo rate 5–19%), those with an odds ratio similar to or greater than that of the US (Portugal, Italy and Spain, adjusted chemo rate 23–41%). Conclusions: In a retrospective analysis of a selected patient population, enrollees in ATAC, nationality was a statistically significant independent predictor for the use of adjuvant chemotherapy. Chemotherapy usage in the US was among the highest of any nation participating in ATAC. We thank Chris Wale for statistical support No significant financial relationships to disclose.