BACKGROUND: The 2 Cohort randomised PrefHer trial examined the preferences of HER2+ve primary breast cancer patients for intravenous (IV) or subcutaneous (SC) delivery of trastuzumab via a Single Injectable Device (SID) or hand-held syringe (HHS). The novel approach and design of the study permitted an in-depth exploration of patients' experiences, the impact that different modes of delivery had on patients' well-being and implications for future management. METHODS: The preferences, experiences and general comments of patients in the PrefHer study were collected via specific semi-structured interview schedules. Exploratory analyses of data were conducted using standard methodology. The final question invited patients to make further comments, which were divided into 9 thematic categories - future delivery, compliments, time/convenience, practical considerations, pain/discomfort, study design, side-effects, psychological impact, and perceived efficacy. RESULTS: 267/467 (57%) patients made 396 additional comments, 7 were neutral, 305 positive and 86 negative. The three top categories generating the largest number of comments were compliments and gratitude about staff and being part of PrefHer (75/396; 19%), the potential future delivery of SC trastuzumab (73/396; 18%), and practical considerations about SC administration (60/396; 15%). CONCLUSIONS: Eliciting patient preferences about routes of administration of drugs via comprehensive interviews within a randomised cross-over trial yielded rich and important information. The few negative comments made demonstrated a need for proper staff training in SC administration Patients were grateful to have been part of the trial, and would have liked to continue with SC delivery. The possibility of home administration in the future also seemed acceptable. EUDRACT NUMBER: 2010-024099-25