Eligibility criteria
| Inclusion | Exclusion | |
| Study design | Primary studies of any design | Systematic reviews, meta-analysis, narrative reviews, letters to the editor, case reports, case series, animal studies, in vitro investigations, studies on human volunteers |
| Population | Patients who underwent surgery for cancer disease | n/a |
| Intervention/exposure | Administration of opioids for the treatment of pain/anaesthesia | n/a |
| Comparator | Methods of opioid-free anaesthesia | No opioids should be administered in the whole perioperative |
| Outcomes | Disease-free survival and/or overall survival | Those other than the chosen outcomes |
| Language | English | Those other than in English |
| Publication status | Published in peer review journals, full-length articles | Published in not peer-review journals, unpublished works as a full-text, abstract, conference meetings |
| Others | All study dates, length of follow-up, setting | n/a |