Background Older patients with cancer often find it difficult to take part in shared decision making. Aim To assess the utility of the Outcome Prioritisation Tool (OPT), designed to aid discussion with a patient in regards to their treatment goals, to empower patients with cancer through structured conversations about generic treatment goals with GPs. Design and setting A randomised controlled trial of 114 Dutch participants recruited between November 2015 and January 2019, aged ≥60 years with non-curable cancer who had to make a treatment decision with an oncologist. The intervention group used the OPT while the control group received care as usual. Method The primary outcome was patient empowerment using the score on the decision self-efficacy (DSE) scale. Secondary outcomes were symptoms measures of fatigue, anxiety, and depression. The experiences of participants were also explored. Results No effect was found on patient empowerment between the OPT group (n = 48; DSE 86.8; standard deviation [SD] = 18.2) and the control group (n = 58; DSE 84.2; SD = 17.6; P = 0.47). In the OPT group, although statistically non-significant, fewer patients had low empowerment (18.8%, n = 9 versus 24.1%, n = 14; P = 0.50), but they did have statistically significant lower mean anxiety scores (6.0, SD = 4.6 versus 7.6, SD = 4.4; P<0.05) and less mild fatigue (58.8%, n = 30 versus 77.2%, n = 44; P = 0.05). Overall, 44.8% (n = 13) of patients indicated that the OPT-facilitated conversation helped them make a treatment decision, and 31.1% (n = 14) of the GPs reported that they gained new insights from the conversation. Conclusion An OPT-facilitated conversation about generic treatment goals between patients and their GPs is associated with less anxiety and fatigue, but did not show statistically significant improvements in patient empowerment. Adding the OPT to routine care might ensure more patient-tailored care.