Background: Teleoncology refers to the use of telemedicine for remotely providing multiple specialized services in clinical oncology processes, including screening, diagnosis, treatment planning, consultation, supportive care, pathology, surgery, and follow-up services. Objectives: The aim of this study was to identify the required data elements and elicitation of requirements for developing a telemedicine system that aims at providing treatment plans for patients with breast cancer. Methods: In this study, the required data elements for the teleoncology system were identified through both the investigation of clinical guidelines and review of patients’ medical records. Identified data elements were determined by breast cancer specialists through the questionnaire. Besides, an interview method was applied to elicit the requirements of this system. Results: The identified data elements were categorized into 20 groups (e.g., clinical data, breast physical examinations, pathological results, tests, imaging results, etc.). From the 182 data elements included within the questionnaire, 125 were recognized to be necessary (n = 32, 100%). The lowest mean percentage were observed in magnesium blood test (Mg) (n = 21, 65.63%) and protein test (Pr) (n = 21, 65.63%). Other data elements with a minimum mean of 71.87% and a maximum mean of 100% were recognized necessary. In general, 2 major themes, 9 categories, and 45 related sub-categories were extracted from analyzing the findings of the interviews related to the system requirements. Conclusions: The findings of the present study can be used as a basis for developing teleoncology systems that aim at providing treatment plans for patients with breast cancer.