Supporting Health Including Endocrine Treatment for Long Duration

Inclusion criteria Participants will be eligible if they meet the following eligibility criteria: * Female * Age 18-49 years at diagnosis of a stage 0-IIIa, HR+ breast cancer * Premenopausal * In active treatment (including long-term endocrine therapy) at the time of enrollment * Able to speak, understand and read English * Access to a US-based mobile phone number * Cognitively able to complete study requirements * Ability to access medical records from treating hospital (DFCI) * Willing to provide cell phone number and/or email address and willing to receive email, mobile push notifications, and/or text messages from the study team Exclusion criteria Participants will be ineligible if they meet any of the following criteria: * Individuals under age 18 or over age 50 at initial breast cancer diagnosis * Stage IV or metastatic breast cancer * Pregnant patients * Individuals who do not have a US mobile phone number * Males with breast cancer are not being recruited to this protocol. In the adolescent and young adult (AYA) age group, only a miniscule proportion of breast cancers occur in males. Additionally, this pilot focuses on breast cancer treatment utilizing OFS and ET, both of which do not apply to males. For this reason, the SHIELD portal intervention materials have been targeted for young women.