1603 Background: SM includes pts’ abilities and activities to manage symptoms, treatment (tx), and any problems inherent to a chronic condition. Tailored SM support is recommended in cancer care. DPM enables pts to systematically self-report disease- or tx-related symptoms, communicate directly with healthcare professionals (HCPs), and access support materials. This observational study evaluated the real-world use of the Symptom Navi Program (SNP; Bern, Switzerland) SM materials on the Kaiku Health DPM platform (Helsinki, Finland) in collaboration with F. Hoffmann-La Roche Ltd (Roche; Basel, Switzerland). Methods: Adults diagnosed with locally advanced or metastatic non-small/small cell lung cancer, or any stage HER2-positive breast cancer being treated with locally approved and reimbursed drugs with an expected tx duration of >3 months, had access to a DPM solution that provided disease- and tx-tailored modules, including SNP SM recommendations for selected mild or moderate symptoms. The co-primary endpoints were DPM adoption and adherence. Here we report secondary endpoints; the perceived clinical impact, DPM module and service experience (assessed via Customer Effort Score [CES] and Customer Satisfaction Score [CSS]), and use of DPM features such as SM recommendations, via a DPM tool questionnaire. Results: Of the 89 enrolled pts, 66 had completed the DPM tool questionnaire at Week 6 of DPM use (data cutoff: June 9, 2022). Among the educational content, the symptom feedback library was accessed most. Pts spent up to a median of 12 minutes on Roche educational or SNP SM materials. The majority of pts (45/66 [68%]) considered the symptom questionnaires to cover all/most of the symptoms they experienced; 18/66 (27%) experienced only fair/partial symptom coverage; 49% (25/51) of pts whose symptoms were not covered contacted their HCP team. 34 pts (52%) took action based on the symptom questionnaire feedback; the most common action was SM recommendations applied according to symptom level (21/66 [32%]), followed by sending a message via the platform to the care team (8/66 [12%]). Half of pts found the SNP SM recommendations helpful/very helpful and 22 pts agreed that the SNP SM recommendations almost always/sometimes supported them in delaying contacting an HCP at an emergency room. At Week 6, the CES was 80%, CSS was 71%, and 48% (32/66) of pts felt that this service improved their care. Conclusions: Pt feedback showed that SNP SM recommendations were the most used action in response to the symptom questionnaire feedback and were perceived by most to be helpful/very helpful. These results support the use of SM recommendations in pts with cancer to help them self-manage tx-related symptoms experienced; future studies are needed to further explore their impact and usefulness, and to form recommendations for routine use in clinical practice.