Clinical implementation of an online family cascade genetic testing platform: The Preventive Risk Outreach and Cascade Testing (PROACT) initiative.

10609 Background: Cascade genetic testing of relatives in families with hereditary cancer susceptibility is an essential strategy to reduce the burden of cancer through targeted risk reduction. However, current testing rates for eligible relatives are low. A promising strategy is to directly engage relatives of affected patients through an online referral service that delivers genetic risk education and the option for home genetic testing to relatives. In the recent GIFT randomized clinical trial, we evaluated an online cascade testing platform for relatives of cancer patients identified through SEER registries. Here, we asked whether a clinical genetic counseling encounter could extend the reach of this approach. Methods: We implemented a pilot project at the Stanford Clinical Cancer Genetics Program that deployed an online hereditary cancer education and germline testing platform for first- and second-degree relatives of patients with a pathogenic or likely pathogenic variant (PV/LPV) in a cancer susceptibility gene. Eligible patients had a germline PV/LPV identified within the past year, spoke English, and had at least one adult first- or second-degree relative in the United States or Canada who had not, to the patient’s knowledge, been tested for the PV/LPV. The virtual family referral service was offered to all eligible patients seen over a six-month period. Primary endpoints were the proportions of eligible relatives in the family who 1) were invited by the enrolled patient through the platform; and 2) ordered testing through the platform (processed by Color Health Inc). Here we report preliminary results from the initial project period; we will report results from the six-month project at time of presentation. Results: Between October 14, 2025 and January 20, 2026, 58 patients with germline PV/LPVs were offered the online tool and 23 patients (40%) enrolled. For these 23 patients, genetic counselors presumptively identified 191 relatives eligible for testing (70 first-degree and 121 second-degree). Patients invited 113 relatives (59%) of whom 57 (50%) accessed the tool and 50 confirmed their eligibility (no prior testing). Among confirmed eligible relatives who accessed the tool, 33 (66%) ordered testing, representing 17% (33/191) of all presumptively eligible relatives. Conclusions: Preliminary results from this clinic-based initiative to deliver cascade genetic testing through an online platform show promise. The findings suggest that an online platform can amplify the clinical genetics encounter and increase cascade testing of relatives in families with hereditary cancer susceptibility. Digital approaches to cascade testing may be particularly impactful for reaching relatives with limited access to care, where traditional cascade testing pathways are challenging. A multi-site clinical trial is planned through the PROACT Initiative.