Adjuvant endocrine hormonal therapy (EHT) is highly effective and appropriate for nearly all breast cancer patients with hormone receptor-positive tumors, which represent 75% of all breast cancer diagnoses. Long-term use of EHT reduces cancer recurrence rates and cuts the risk of death nearly in half during the second decade after diagnosis, research shows. Despite the proven benefits, about 33% of women who are prescribed EHT do not take their medication as prescribed (less than 80% take their daily dosage) and are thus at higher risk of recurrence and death. This educational randomized controlled study will develop and pilot-test a bilingual, culturally tailored, personalized, interactive mobile application (app) in combination with patient navigation to promote and improve adherence to endocrine hormonal therapy (EHT) among breast cancer patients.