Aim: To evaluate the quality of life (QoL) in patients with breakthrough cancer pain (BTcP) in Spanish medical oncology departments. Patients & methods: In a prospective, observational, multicenter study, we assessed QoL using the EQ-5D-5L instrument at baseline and after 15 and 30 days of individualized BTcP therapy, as well as BTcP characteristics and treatment. Results: Patients (n = 118) were mainly women, over 64 years old and with advanced cancer. QoL improved at 15 (p = 0.013) and 30 days (p = 0.011) versus baseline. Individualized BTcP therapy consisted mostly of rapid-onset opioids (transmucosal fentanyl at doses of 67-800 μg) according to the physician evaluation. BTcP improved, including statistically significant reductions in intensity, duration, number of episodes in the last 24 h and time to onset of BTcP relief. Conclusion: QoL increased after individualized pain therapy in patients with advanced cancer and BTcP in medical oncology departments. Keywords: breakthrough cancer pain; medical oncology; quality of life; rapid-onset opioids; transmucosal fentanyl.