In recent years, we have conducted an international collaborative trial for neuropathic cancer pain between Japan and Australia (protocol published in BMJ Open, 2022), as well as a domestic study on delirium prevention (protocol published in Jpn J Clinical Oncology, 2023). This presentation reflects on the challenges encountered in the former trial, in contrast to the smooth implementation of the latter, and offers insights for improving future clinical research. A key challenge was the difference in clinical practice. In Japan, neuropathic cancer pain is typically managed by titrating opioids before introducing adjuvant analgesics, whereas in Australia, adjuvant analgesics are often used early, even without opioid administration. This discrepancy made patient recruitment difficult. Differences in dosing strategies between Japan and Australia also presented challenges in trial implementation. Another issue was the prescribing authority. In Japan, palliative care teams usually make treatment recommendations rather than prescribe directly, requiring extensive coordination with oncology teams. As a result, trial initiation demanded careful interdepartmental collaboration. Despite these challenges, patient recruitment in Australia improved following site visits and ongoing discussions, ultimately leading to the successful completion of our international collaborative study. In the subsequent delirium prevention trial conducted in Japan, we applied lessons learned by allocating sufficient time in advance to thoroughly explain the study to nurses across all wards and to members of all clinical departments. As a result, we were able to complete patient enrollment within approximately two years, despite an unexpected suspension due to a patient’s death during the study period. We hope these experiences will contribute to the advancement of future international collaborative research in the fields of palliative care and psycho-oncology. I hope these experiences will help inform future international collaborative research in the fields of palliative care and psycho-oncology.