Background: Biomarkers for predicting immune checkpoint inhibitor (ICI) efficacy are essential for patient selection for current ICI regimens and new combination therapies. Patients with T-cell excluded tumors have poor effect on ICI therapy. T-cell exclusion is driven by upregulated TGF-β-signaling and activated fibroblasts, which produce increased levels of fibrillar collagens (desmoplasia). In this study, we investigated if non-invasive biomarkers reflecting deposition of the fibrillar collagen type III (PRO-C3) and collagen type XI (PRO-C11) associated with response and survival outcomes in patients treated with ICI therapy.

Methods: N-terminal pro-peptides of collagen type III (PRO-C3) and collagen type XI collagen (PRO-C11) were measured with ELISAs in pre-treatment serum from metastatic melanoma patients treated with anti-PD-1 therapy (pembrolizumab) (n=35). The association between PRO-C3 and PRO-C11 levels and progression-free survival (PFS) and overall survival (OS) were assessed by Cox regression analyses, alone and after adjusting for tumor PDL1 expression and BRAF mutational status.

Results: Univariate Cox regression identified high (<75th percentile) baseline PRO-C3 and PRO-C11 as predictors of poor PFS (PRO-C3: HR=2.77, 95%CI=1.01-7.55, p=0.047, and PRO-C11: HR=2.87, 95%CI=1.05-7.87, p=0.040) and OS (PRO-C3: HR=6.54, 95%CI=1.56-27.53, p=0.010, and PRO-C11: HR=4.58, 95%CI=1.13-18.65, p=0.034). Moreover, when PRO-C3 and PRO-C11 were adjusted for PDL1 expression (≥1%) and BRAF mutations, the biomarkers remained independently predictive of poor PFS (PRO-C3: HR=3.00, 95%CI=1.07-8.42, p=0.038, and PRO-C11: HR=3.66, 95%CI=1.22-10.98, p=0.021) and OS (PRO-C3: HR=6.20, 95%CI=1.47-26.12, p=0.013, and PRO-C11: HR=7.85, 95%CI=1.32-46.78, p=0.024). PRO-C3 was furthermore significantly elevated in patients with progressive disease compared to patients with complete response, partial response and stable disease (p=0.007).

Conclusions: Non-invasive biomarkers of the fibroblast-derived collagen type III (PRO-C3) and collagen type XI (PRO-C11) reflecting fibroblast activity predict survival outcomes in metastatic melanoma patients treated with anti-PD-1 therapy independent of PD-L1 expression and BRAF mutational status. These findings support the link between desmoplasia (tumor fibrosis) and poor response to ICIs and indicate a promise of non-invasive collagen-based biomarkers for selecting metastatic melanoma patients for anti-PD-1 therapy at baseline and hereby improve the response rate.

Citation Format: Christina Jensen, Anders Kverneland, Marco Donia, Neel I. Nissen, Morten A. Karsdal, Inge Marie Svane, Nicholas Willumsen. Non-invasive biomarker potential of the fibroblast-derived collagen type III and collagen type XI for predicting outcome in metastatic melanoma patients treated with anti-PD-1 therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 388.