Real-world experiences with a multi-cancer detection (MCD) blood test.

10565 Background: Multi-cancer detection (MCD) blood tests hold promise to screen for multiple cancers simultaneously. MCD tests have been assessed in case-control and prospective studies but have not yet been shown to improve cancer outcomes. Mass General Brigham (MGB) offers a commercially available, non-FDA-approved methylation-based MCD test (Galleri; GRAIL) through our Early Detection most were White (92%) and up to date on USPSTF-recommended cancer screening (82%). Med follow up (FU) was 469 days (IQR 462-478); 580 (78%) had > 12 months FU. Four pts received a “cancer signal detected” result (+MCD): 2/742 tested at MGB (0.3%) and 2 who presented to workup +MCD tested elsewhere; 2 were true positives (TP), 2 false positives. In total, 16 pts (2.2%) were diagnosed (dx) with cancer during FU; 2/16 (13%) after +MCD, and 14/16 after negative MCD, with med time from MCD to diagnosis 199 days (IQR 92-464). The two TP tests corresponded to stage I breast cancer and stage III follicular lymphoma. The most common cancers dx were prostate (n = 5, with two stage III-IV dx at 128 and 142 days) and breast (n = 4, all mammogram-detected stage I). Other advanced cancers included stage III cholangiocarcinoma and stage IV adenocarcinoma unknown primary (dx at 515 and 475 days, respectively). Conclusions: In this real-world cohort, MCD test positivity was rare, and multiple cancers were dx within 18 months of a negative MCD, including some advanced cases. In particular, prostate cancer was dx in multiple pts after negative MCD, consistent with prior reports of limited MCD sensitivity for prostate cancer. Our cohort may be biased by the requirement to either self-pay or carry a specific insurance product. Larger studies with longer FU are needed to better define the added utility of MCD tests to standard cancer screening.