Hormonal therapy is an effective yet challenging long-term treatment for patients with hormone receptor positive breast cancer. Understanding what factors indicate discontinuation of a recommended hormonal therapy medication can help improve treatment experience. To date, studies on medication discontinuation have focused on patient information gathered through questionnaires, structured electronic medical records and online discussion boards. However, there has been little investigation into the communications between healthcare providers, which may provide additional indicators of patients' medication discontinuation, particularly from a clinical perspective. In this paper, we investigate the relation between such communications and hormonal therapy medication discontinuation. We studied a cohort of 2,579 patients on hormonal therapy at the Vanderbilt University Medical Center over a 16-year period. We adopt a data-driven approach to investigate the clinical messages communicated by their healthcare providers, the messaging patterns, topics they communicated, and the extent to which these factors are affiliated with discontinuation to a recommended 5-year treatment protocol. Our findings suggest that notification of unread messages, plans for clinical trials and the occurrence of treatment-related complications are affiliated with an increased risk of medication discontinuation. By contrast, ordering prescriptions, making appointments, using positive communication verbs, and noting patients' stable health conditions are affiliated with a decreased risk of medication discontinuation.