Background: We examined time trends of CT used and associations with pts characteristics in Stage I BC. Methods: Prospective cohort studyincluding pts with Stage I BC treated at a National Comprehensive Cancer Network center from 2000-09. We examined the proportion of pts receiving intensive vs. non-intensive CT over time.We defined an intensive regimen as: a combination of anthracyclines and taxanes (e.g. ACT ± H) or a combination of carboplatin and docetaxel (e.g. TCH), and non-intensive as: anthracycline-based (e.g. AC), taxane-based (e.g. TC) or similar. We evaluated factors associated with type of CT using multivariable logistic regression. Analyses were stratified by HER2 receptor status. Results: Of 8,907 pts, 33% received adjuvant CT. There was a dramatic increase of intensive CT: among HER2+ pts from 31% in 2000-05 to 63% in 2008-09 (including an increase in the use of TCH) and among HER2- from 15% in 2000-05 to 41% in 2008-09. Among non-intensive regimens there was an increase in the use of regimens such as TC with a parallel decrease in the use of regimens such as AC, in both HER2+ and HER2- groups. Characteristics which factored into CT decisions differed by tumor subtype, with significant center variations. Conclusions: Over time, there was an increase in use of intensive regimens among Stage I BC. CT use differed by HER2 status with striking center and temporal variations.

Among pts receiving *TCH/ACTH (represents 53% of pts with HER2+disease ). ^# TC/AC ( 68% of pts with HER2- disease).