Abstract Background Aside from chemotherapy utilization, limited data are available on the relationship between gene expression profiling (GEP) testing and breast cancer care. We assessed the relationship between GEP testing and additional variables and the outcomes of endocrine therapy initiation, discontinuation and adherence, and breast imaging exams in women under age 65 years. Methods Data from five state cancer registries were linked with claims data and GEP results. We assessed variables associated with survivorship care outcomes in an incident cohort of 5014 commercially insured women under age 65 years, newly diagnosed with stage I or II hormone-receptor-positive, human epidermal growth factor receptor 2 (HER2) non-positive breast cancer from 2006 to 2010. Results Among tested women, those with high Oncotype DX® Breast Recurrence Score® (RS) were significantly less likely to initiate endocrine therapy than women with low RS tumors (OR 0.40 (95% CI 0.20 to 0.81); P = 0.01). Among all test-eligible women, receipt of Oncotype DX testing was associated with a greater likelihood of endocrine therapy initiation (OR 2.48 (95% CI 2.03 to 3.04); P <0.0001). The odds of initiation were also significantly higher for tested vs. untested women among women who did not initiate chemotherapy within six months of diagnosis (OR 3.25 (95% CI 2.53 to 4.16)), with no effect in women who received chemotherapy. Discontinuation and adherence and breast imaging exams were unrelated to tested status or RS. Conclusions Lower endocrine therapy initiation rates among women with high RS tumors and among untested women not receiving chemotherapy are concerning, given its established efficacy. Additional research is needed to suggest mechanisms to close this gap.