Transmucosal fentanyl (TF), used for breakthrough cancer pain (BTcP) treatment, has different formulations with distinctive attributes. The hypothesis is that, in shared decision making for the prevention of certain therapeutic problems, doctors and patients assign different value to the characteristics of treatment options. The aim of this study was to assess the discordance between the oncologists' opinion of attributes of TF and patients' expectations in BTcP treatment. This is a multicenter, cross-sectional observational study using simultaneous written surveys of doctors and patients suffering from BTcP episodes. The opinion of Spanish oncologists and patients regarding the importance of 14 different attributes of TF treatment (start of action, potency, duration, presentations and doses available, ease of use, titration, administration time, need for saliva, oral mucositis, rhinitis, adverse events, risk of abuse, evidence available, and need for instructions or health personnel to handle the medication), using two surveys, one for each group. Sixty-three clinical oncologists and 272 patients participated in the study. The patients' satisfaction with and knowledge of BTcP treatment was 6.4 and 6.8 points, respectively (scale 1-9). The attributes with the highest relevance were shared by both groups, although their priority differed. Significant differences were observed in the greater importance given by oncologists (onset and duration of analgesia, need for saliva, presence of mucositis, and time required for patient education) and patients (risk of opioid abuse/aberrant behavior). Our results confirm that some aspects that most concern patients about the treatment of BTcP differ from those to which oncologists attach most importance. Increased patient awareness and education about BTcP and its treatment could lead to greater satisfaction and better patient involvement in therapeutic decisions. Certain barriers need to be overcome, such as lack of time in consultations and poor communication skills of oncologists that hinder patient health education.