Abstract
Diphencyprone (DPCP), a topical contact sensitizer, has shown efficacy in treating cutaneous melanoma metastases, including at times beyond the directly treated sites, but biomarkers indicative of treatment response have not been characterized. Thus, we performed a proteomic analysis of the skin and serum of five patients with cutaneous melanoma metastases treated with DPCP on days 0, 63, and 112 of the treatment course. In the serum, we found a significant upregulation (P < 0.05) in 13 of 96 assessed immuno-oncology proteins after DPCP treatment. Upregulated proteins included those of the T helper 1 axis (CXCL9, CXCL10), immune checkpoint proteins (PD-1), and various proteins with roles in promoting tumor immunity such as CD80 and TNFRSF4/9. Given the positive clinical response to topical treatment noted in the five patients studied, these proteins may represent prognostic biomarkers in the serum for evaluating the efficacy of DPCP treatment of cutaneous melanoma metastases. Because DPCP does not lead to nonspecific immune-related adverse events seen with immune checkpoint inhibitors, our study provides evidence for potential tumor-specific systemic immune activation and systemic antitumor effectors elicited by topical DPCP.