Breakthrough cancer pain is divided into "predictable breakthrough pain" and "unpredictable breakthrough pain". Uncontrolled breakthrough pain in cancer negatively affects the quality of life of the patients. The short-acting opioid(SAO) requires considerable time to produce analgesia, and is not adequate as a rescue drug. The rapid-onset opioid(ROO)immediately produces analgesia, but its appropriate usage is difficult. For instance, the frequency and interval of ROO usage is limited, making the optimization of dosage cumbersome. Therefore, ROO has not yet gained popularity. Here, we report that a combinatorial use of ROO and SAO is effective against breakthrough cancer pain, with SAO and ROO being suitable for "predictable breakthrough pain", and "unpredictable breakthrough pain", respectively. The effectiveness and safety of this combination were assessed for many patients with breakthrough cancer pain.