Background: Opioids have been the cornerstone of analgesic treatment for severe chronic pain. OIC is the most commonly reported adverse effect associated with opioids, and compromises patient satisfaction and adherence to analgesic treatment and also quality of life. Naloxegol is a PEGylated derivative of the µ-opioid receptor antagonist naloxone indicated for the treatment of opioid-induced constipation (OIC) in adult patients who have had an inadequate response to laxatives. This real-world (RW) study (NCT03638440) aims to evaluate safety and efficacy of Naloxegol in patients with cancer pain diagnosed with OIC. Methods: This is a single-arm, multinational, prospective, RW observational study in adult subjects receiving treatment with opioids for at least 4 weeks, diagnosed with OIC that receive naloxegol in routine clinical practice. This study will recruit patients from 25 European hospitals. Data for efficacy are collected through the patient's diary during a 4-week period. Results: One hundred fifty-two patients, median age 66 years, 54% women, have been included in this analysis. Main cancer locations were lung (26%), breast (21%), prostate (10%), pancreas (9%) and head and neck (9%), and 67% had metastasis, mainly in bone (37%). Most frequent opioid treatments were fentanyl (29%), oxycodone (22%), and morphine (15%). Most frequent previous laxatives were osmotic (61%) and stimulant (27%) laxatives. Over 109 patients with at least one BFI score available after baseline, change in BFI score was ≥12 points in 61% of patients and 33% had BFI score <30 points after 4 weeks of treatment. There were statistically significant differences between baseline and final visit in BFI overall score as well as in the score of each of the three questions. Most common adverse reactions to naloxegol were abdominal pain (7.9%), diarrhea (2.6%), flatulence (1.3%) and nausea (1.3%), most of them grade 1-2. Eight patients had adverse reactions leading to study discontinuation: abdominal pain (5), diarrhea (2), intestinal perforation (1) and fatigue (1). Only one patient died due to an adverse reaction: intestinal perforation. Conclusions: Preliminary results show a promising efficacy of naloxegol in this RW treatment study. Toxicity profile was as expected. RW evidence seems to be a useful methodology to assess the real-life use of naloxegol and its efficacy in cancer patients.