Objective: Prospective cohort study to test the real-life feasibility of longitudinal patient-reported outcome measurement PROM (Integrated Palliative Outcome Scale IPOS, and NCCN Distress Thermometer DT) required for outpatients with non-curable lung or prostate cancer in comprehensive cancer centers., Methods: Assessment with paper-based IPOS and DT was observed for 15 months. We analyzed response to patients' distress (requests for supportive and palliative services) following PROM. Focus groups to comprehensively explore the user experience of patients, informal caregivers and health care professionals (HCP) supplemented the analysis., Results: Ninety-seven percent (125/129) of the patients received a questionnaire once, but quarterly assessment as recommended by certification committees was achieved only in 50% and 31% of prostate and lung cancer patients. Although both instruments were well accepted, only IPOS showed a high content validity, because some patients had difficulties in understanding the DT. Patients felt comfortable with completing the PROM, and HCP found PROM helped to structure the patient encounter. Due to organizational deficiencies in the handling of the instruments and operationalization of reactions to identified distress, the referrals to supportive and palliative services were rare., Conclusion: To facilitate consequences from PROM it should be a standardized intervention rather than assessment alone., Innovation: The patient perspective improves the implementation of PROM under real-life clinical conditions., Competing Interests: The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Christina Gerlach reports a relationship with Amgen that includes: consulting or advisory., (© 2024 The Authors.)