A plasma-based proteomic platform for predicting clinical benefit from immune checkpoint inhibitors in multiple cancers.

2568 Background: Immune checkpoint inhibitor (ICI)-based therapies are preferred treatment options for multiple cancer types. However, there is an unmet need for predictive tests that can identify patients likely to benefit. PROphet-NSCLC is a commercially available pretreatment plasma proteomic test that predicts clinical benefit from first-line PD-(L)1 inhibitor-based therapy in patients with metastatic non-small cell lung cancer (NSCLC), guiding the choice between ICI monotherapy versus ICI-chemotherapy. Here, we evaluate the broader clinical utility of PROphet-NSCLC by testing its predictive capabilities across diverse cancer types. Methods: Pre-treatment plasma samples and clinical data were collected for an observational study from patients with metastatic melanoma (n=68) and HPV-related cancers (n=43; NCT03427411) treated with PD-(L)1 inhibitor-based therapies. HPV-related cancers included anogenital squamous cell carcinoma (n=16), cervical carcinoma (n=18), and head and neck squamous cell carcinoma (n=9). Patients were assigned a PROphet-positive or -negative result based on computational analysis of SomaScan-derived proteomic profiles in pre-treatment plasma samples. Overall survival (OS) and progression-free survival (PFS) in PROphet-positive- and -negative groups was analyzed with the Kaplan-Meier method. Hazard ratios (HR) were calculated from univariate and multivariate Cox proportional hazard models. Results: In the melanoma cohort, PROphet-positive patients (n=51) displayed a significant OS benefit in comparison to PROphet-negative patients (n=17; median OS 92.8 months vs. 9.5 months, HR=0.14, 95% CI: 0.06-0.34, p<0.0001), consistent with the clinically validated predictive performance of the test in patients with NSCLC. OS results remained significant after correcting for sex, age, histology, ECOG performance status, and treatment type (HR=0.05, 95% CI: 0.01-0.25, p<0.001). In PROphet-positive patients, PD-1+CTLA-4 inhibitor combination therapy (n=27) was superior to PD-1 inhibitor monotherapy (n=24; OS: median 118.4 vs. 48.3 months, HR=0.58, p=0.24; PFS: median not reached vs. 10.8 months, HR=0.48, p=0.04). PROphet-negative patients displayed similarly poor outcomes with either treatment, providing a rationale to consider alternative therapies for such patients. In the HPV-related cohort, the median OS in PROphet-positive (n=10) vs PROphet-negative (n=33) groups was 43.6 vs 4.4 months (HR=0.22, 95% CI: 0.08-0.59, p=0.001), with similar trends per sub-cohort. Conclusions: Our findings show that the PROphet-NSCLC test can be applied to PD-(L)1 inhibitor-treated melanoma and HPV-related cancers, suggesting applicability to cancers beyond NSCLC. Analysis of additional patient samples is needed to explore the potential utility of PROphet-NSCLC for informing treatment decisions for a broad range of cancer types.